This section has 4 verses.
 
Titus 3:8-11
8 This is a faithful saying, and these things I will that thou affirm constantly, that they which have believed in God might be careful to maintain good works. These things are good and profitable unto men.
9 But avoid foolish questions, and genealogies, and contentions, and strivings about the law; for they are unprofitable and vain.
10 A man that is an heretick after the first and second admonition reject;
11 Knowing that he that is such is subverted, and sinneth, being condemned of himself.
 
We will begin with the Barclay commentary.

THE NECESSITY OF ACTION AND THE DANGER OF DISCUSSION

First, the paraphrase of verses 8-11:

This is a saying which we are bound to believe – and I want you to keep on affirming these things – that those who have put their faith in God must think and plan how to practice fine deeds. These are fine things and useful to men. But have nothing to do with foolish speculations and genealogies and contentious and legalistic battles, for they are no good to anyone and serve no useful purpose. Avoid a contentious and self-opinionated man, after giving him a first and a second warning, for you must be well aware that such a man is perverted and stands a self-condemned sinner.

THIS passage stresses the need for Christian action and the danger of a certain kind of discussion.

The word we have translated as to practice fine deeds is proistasthai, which literally means to stand in front of and was the word used for a shopkeeper standing in front of the shop and calling out to advertise the produce. The phrase may mean either of two things. It might be a command to Christians to engage only in respectable and useful trades. There were certain professions which the early Church insisted that people should give up before they were allowed even to ask for membership. More probably, the phrase has the wider meaning that Christians must practice good deeds which are helpful to others.

The second part of the passage warns against useless discussions. The Greek philosophers spent their time on their over subtle [over precise, picky, hair-splitting] problems. The Jewish Rabbis spent their time building up imaginary genealogies for the characters of the Old Testament. The Jewish scribes spent endless hours discussing what could and could not be done on the Sabbath, and what was and was not unclean. It has been said that there is a danger that people might think themselves religious because they discuss religious questions. It is much easier to discuss theological questions than to be kind and considerate and helpful at home, or efficient and conscientious and honest at work. There is no virtue in sitting discussing deep theological questions when the simple tasks of the Christian life are waiting to be done. Such discussion can be nothing other than avoidance of Christian duties.

Paul was certain that the real task for Christians lay in Christian action. That is not to say that there is no place for Christian discussion; but the discussion which does not end in action is very largely wasted time.

It is Paul’s advice that contentious and self-opinionated people should be avoided. The Authorized Version calls that kind of person the heretic. The Greek is hairetikos. The verb hairein means to choose, and hairesis means a party, or a school or a sect. Originally, the word carried no bad meaning. This creeps in when someone sets private opinion against all the teaching, the agreement and the tradition of the Church. Heretics are simply people who have decided that they are right and everybody else is wrong. Paul’s warning is against those who have made their own ideas the test of all truth. We should always be very careful of any opinion which separates us from the fellowship of our fellow believers. True faith does not divide people; it unites them. ~Barclay Commentary

Note: Heretic
A professed believer who maintains religious opinions contrary to those accepted by his or her church or rejects doctrines prescribed by that church [from the Word of God].

Now to the other commentaries. We will begin with the general and move to the specific. We go to the Matthew Henry Main. The commentary covers verses 1-8 as one section. I will pick it up where it speaks of verse 8.

III. The apostle, having opened the duties of Christians in common, with the reasons respecting themselves, adds another from their goodness and usefulness to men. Observe, When he has opened the grace of God towards us, he immediately presses the necessity of good works; for we must not expect the benefit of God's mercy, unless we make conscience of our duty (Titus 3:8): This is a faithful saying, and these things I will that thou affirm constantly (this is a true Christian doctrine of highest importance, and which ministers must most earnestly and constantly press [weigh heavily upon] and inculcate [to implant by repeated statement or admonition; teach persistently and earnestly ]), that those who have believed in God do not think that a bare naked faith will save them; but it must be an operative [having force; being in effect or operation] working faith, bringing forth the fruit of righteousness; they must make it their care to maintain good works, not to do them occasionally only, and when opportunities come in their way, but to seek opportunities for doing them. These things are good and profitable unto men: these good works, say some, or the teaching of these things, rather than idle questions, as follows. These things are good in themselves and the teaching of them useful to mankind, making persons a common good in their places. Note, Ministers, in teaching, must see that they deliver what is sound and good in itself, and profitable to those that hear: all must be to the use of edifying both of persons and societies. ~Matthew Henry Main

Note: Where the commentary says, "they must make it their care to maintain good works, not to do them occasionally only, and when opportunities come in their way, but to seek opportunities for doing them." God works it this way: He creates the opportunities, so where the commentary says, "when opportunities come in their way" we are referring to God bringing opportunities constantly. Where is says, "but to seek opportunities for doing them" we are speaking of you and I constantly looking for and acting upon the many opportunities God is purposefully putting in our path.

Now to the Matthew Henry Concise which covers this section of verses 8-11:

When the grace of God towards mankind has been declared, the necessity of good works is pressed. Those who believe in God, must make it their care to maintain good works, to seek opportunities for doing them, being influenced by love and gratitude. Trifling, foolish questions must be avoided, and subtle distinctions and vain inquiries; nor should people be eager after novelties, but love sound doctrine which tends most to edifying. Though we may now think some sins light and little, if the Lord awaken the conscience, we shall feel even the smallest sin heavy upon our souls. ~Matthew Henry Concise

Note: There is no such thing as "the smallest sin." This concept of being "eager after novelities" is speaking to new doctrines and weird ideas someone might wish you to look into. We are not necessarily speaking to breaking news stories or even a person's speculation, opinion or conspiracy theory about news and events which revolve around established doctrine and/or prophecy but rather anything to do with new doctrine. In the 14th century, this is what they said for the word, "novelty": "Meaning 'newness" is attested from late 14th century; sense of 'useless but amusing object.' " In other words, people might bring you subjects that are amusing and even exciting, but they are, as it says, "useless.' We will confirm this in the next verse [Verse 9].

Now something from the Biblical illustrator:

Good works
I. Define good works.

1. That our works may be good, they must be
(1) Performed by good persons;
(2) Required by God’s Word;
(3) Done from a sound principle;
(4) Done to a right end.

2. How these good works must be maintained
(1) Attention to God’s Word;
(2) Solicitude to know God’s mind;
(3) Watchfulness against temptations;
(4) Embracing every opportunity of doing good;
(5) Pressing forward in knowledge;
(6) Exciting others to do the same.

II. The faith which produces good works.

1. Knowledge of God.
2. And of the Word of God.
3. Faith is a composing grace.
4. A receptive grace.
5. An operative grace.
6. A rooting grace.
7. A humbling grace.
8. An elevating grace.
9. A strengthening grace.
10. A uniting grace.
11. A working grace.
12. A saving grace.

III. How good works are profitable to men.
1. As evidences of true faith.
2. Testimonies of gratitude to God.
3. Strengthening to assurance.
4. Edifying to others.
5. Condemning the world. ~Biblical Illustrator

Practical Christianity
I. Practical Christianity is good in itself.
1. It accords with the will of God.
2. It is an object of moral approbation to all minds.

II. Good in its influence. Nothing is so useful to men as a Christly life. ~Biblical Illustrator

Some hints to preachers
I. Fundamental truths are to be continually enforced.

II. Practical preaching is ever out of season.

III. Christian duties are of universal application.

IV. Trivial questions out of place in the pulpit. Inferences
1. It is possible to have repetition without sameness: “affirm constantly.”
2. Belief that does not change the life is useless (James 2:17)
3. The law is to be obeyed in spirit, rather than letter. ~Biblical Illustrator

Quoted verse:
James 2:17
Even so faith, if it hath not works, is dead, being alone.

Now to the specific commentaries. This verse is generally broken out in 4 parts.

1] This is a faithful saying.
2] And these things I will that thou affirm constantly.
3] That they which have believed in God might be careful to maintain good works.
4] These things are good and profitable unto men.

1] This is a faithful saying.

This is a faithful saying - See the notes at 1 Timothy 1:15. The reference here is to what he had been just saying, meaning that the doctrine which he had stated about the method of salvation was in the highest degree important, and entirely worthy of belief. ~Barnes Notes

Quoted verse:
1 Timothy 1:15 [see Lesson]
This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief.

This is a faithful saying - This is the true doctrine; the doctrine that cannot fail. ~Adam Clarke

This is a faithful saying - Meaning the whole of what is before expressed, concerning the state and condition of God's elect by nature; the appearance of the love and kindness of God to them in the effectual calling; the salvation of them, according to the mercy of God, and not by works of righteousness; regeneration, and renovation by the Spirit of God, in which such an abundance of grace is communicated; and justification by the free grace of God, as God's way of salvation; and by which men are made to appear to be heirs of eternal life, and to have hope of it: now all, and each of this is a faithful saying, is true doctrine, and to be believed, professed, and published: wherefore it follows. ~John Gill

2] And these things I will that thou affirm constantly.

And these things I will that thou affirm constantly - Make them the constant subject of your preaching. “That they which have believed in God might be careful to maintain good works.” This shows that Paul supposed that the doctrines of the gospel were fitted to lead people to holy living; compare Titus 3:1, and the notes at Philippians 4:8. The “good works” here refer not merely to acts of benevolence and charity, but to all that is upright and good - to an honest and holy life. ~Barnes Notes

Quoted verses:
Titus 3:1 [see Lesson]
Put them in mind to be subject to principalities and powers, to obey magistrates, to be ready to every good work.

Philippians 4:8
Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things.

And these things I will that thou affirm constantly - And I will, or desire, thee to maintain earnestly what concerns these points. The things to which the apostle refers are those of which he had just been writing, and may be thus summed up:

1. The ruined state of man, both in soul and body.
2. The infinite goodness of God which devised his salvation.
3. The manifestation of this goodness, by the incarnation of Jesus Christ.
4. The justification which they who believed received through his blood.
5. The mission of the Holy Spirit, and the purification of the heart by [its] influence.
6. The hope of the resurrection of the body, and the final glorification of both it and the soul through all eternity.
7. The necessity of obedience to the will of God, and of walking worthy of the vocation wherewith they had been called.
8. And all these points he wills him to press continually on the attention of believers; and to keep constantly in view, that all good comes from God’s infinite kindness, by and through Christ Jesus. ~Adam Clarke

And these things I will that thou affirm constantly - that is, the above doctrines; the Arabic version renders it, "I will that thou be firm in these things"; and the Syriac and Ethiopic versions, "I will that thou confirmest them": the sense of the apostle is, that he would have Titus be assured of those truths himself; be at a point about them, and without any doubt or hesitation concerning them; and abide firm and constant in them, and speak of them with certainty, boldness, and confidence to others; and endeavour to confirm and establish them in them: for which purpose he would have them be frequently inculcated and insisted on; and that with this further view. ~John Gill

3] That they which have believed in God might be careful to maintain good works.

That they which have believed in God might be careful to maintain good works. - All Christians; for who can maintain good works but those who have the principle from which good works flow, for without faith it is impossible to please God. ~Adam Clarke

Note: In other words, those that primarily maintain good works are individuals in the salvation process and the fruits of the Spirit we invoke or manifest there.

That they which have believed in God might be careful to maintain good works. - "by good works", are meant, not merely honest trades, and the lawful occupations and businesses of life, which should be carefully attended to, and diligently followed, in order to be useful and profitable to themselves, their families, and others; but every good work, every branch of duty, moral, civil, and religious: to "maintain" these according to the signification of the word used, is to excel in them; to outdo others; to go before others, by way of example, and so to provoke to love and to good works; and to make them the employment and business of men's lives; for which there should be a thoughtfulness, a carefulness, a studious concern, especially in those who "have believed in God." ~John Gill

4] These things are good and profitable unto men.

These things are good and profitable unto men - That is, these doctrines which he had stated were not mere matters of speculation, but they were fitted to promote human happiness, and they should be constantly taught. ~Barnes Notes

These things are good and profitable - They are good in themselves, and calculated to promote the well-being of men. ~Adam Clarke

These things are good and profitable unto men - which is to be understood not of good works, though these are good in themselves, and profitable to men in their effects; being done among them, and before them, they set them an example of doing good likewise, when evil communications corrupt good manners; and many of them issue in their temporal good, profit, and advantage: but rather the doctrines of the Gospel are here designed, which are before briefly treated of, and are said to be a faithful saying; and which the apostle would have affirmed with, certainty and constancy, in order to engage believers to the performance of good works; and that for this reason, because these doctrines are "good", excellent, valuable, and precious, comparable to gold, silver, and precious stones: the author, matter, end, and use of them are good; they come from God; they are concerning Jesus Christ, and his grace; they contain good tidings of good things; and are exceeding useful to influence faith, hope, love, and a cheerful obedience to the will of God: they are profitable for conviction, conversion, comfort, and edification; for the quickening and enlightening of dead and dark sinners; for the reviving, establishing, and building up of the saints; they are the wholesome words of Christ, and are according to godliness, and are nourishing, when other doctrines eat as a canker: and this sense is confirmed, not only by what goes before, but by what follows after in the next verse; where insipid notions and controversies are opposed unto them, as unprofitable and vain. ~John Gill

So,
1] Speak evil of no man.
2] Understand that you were once foolish, disobedient and deceived.
3] God came with the salvation process for all of mankind.
4] Salvation is not attained by good works.
5] Good works are the classroom for learning the principles of God
6] We are saved by the grace of God and by the shed blood of Jesus Christ.
7] Those who believe in God are careful to maintain good works and built the character of Christ.

All these things are a faithful saying and are good and profitable unto mankind.  This is the lesson of verse 8