This section has 1 verse.
 
Titus 2:15
These things speak, and exhort, and rebuke with all authority. Let no man despise thee.
 
 We will begin with the Barclay commentary.
 
THE THREEFOLD TASK

First the verses paraphrased:
 
Titus 2:15
Let these things be the substance of your message. Deal out encouragement and rebuke with all the authority which your royal commission confers upon you. Let no one regard your authority as cheap.

HERE, Paul succinctly lays before Titus the threefold task of every Christian preacher, teacher and leader.

It is a task of proclamation. There is a message to be proclaimed. There are some things about which argument is not possible and on which discussion is not relevant. There are times when the only thing to say is: ‘Thus says the Lord.’

It is a task of encouragement. Any preacher who reduces an audience to bleak despair has failed. People must be charged with their sin, not so that they may feel that their case is hopeless, but that they may be led to the grace which is greater than all their sin.

It is a task of conviction. The eyes of sinners must beopened to their sin; the misguided must be led to realize their mistakes; the hearts of the inconsiderate must be pricked into awareness. The Christian message is no drug to send us to sleep; it is rather the blinding light which shows us our true selves as we really are and God as he is. ~Barclay Commentary
 
Now to the other commentaries. We begin with the general and go to the specific.

Here is the Matthew Henry Main:

The apostle closes the chapter (as he began it) with a summary direction to Titus upon the whole, in which we have the matter and manner of ministers' teaching, and a special instruction to Titus in reference to himself.

I. The matter of ministers' teaching: These things, namely, those before mentioned: not Jewish fables and traditions, but the truths and duties of the gospel, of avoiding sin, and living soberly, righteously, and godly, in this present world. Observe, Ministers in their preaching must keep close to the word of God. If any man speak, let him speak as the oracles of God, 1 Peter 4:11, and not the figments and inventions of his own brain.

Quoted verse:
1 Peter 4:11
If any man speak, let him speak as the oracles of God; if any man minister, let him do it as of the ability which God giveth: that God in all things may be glorified through Jesus Christ, to whom be praise and dominion for ever and ever. Amen.

II. The manner; by doctrine, and exhortation, and reproof with all authority. 2 Timothy 3:16, All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, and for instruction in righteousness; that is, to teach sound doctrine, to convince of sin and refute error, to reform the life, and to carry forward in what is just and good; that the man of God (the Christian or minister) may be perfect, thoroughly furnished to all good works that are to be practiced by himself or to be taught to others. Here is what will furnish for all parts of his duty, and the right discharge of them. “These things speak, or teach; shun not to declare the whole counsel of God.” The great and necessary truths and duties of the gospel, especially, these speak and exhort, parakalei, press with much earnestness. Ministers must not be cold and lifeless in delivering heavenly doctrine and precepts, as if they were indifferent things or of little concern; but they must urge them with earnestness suitable to their nature and importance; they must call upon persons to mind and heed, and not be hearers only, deceiving themselves; but doers of the word, that they may be blessed therein. And rebuke; convince and reprove such as contradict or gainsay, or neglect and do not receive the truth as they should, or retain it in unrighteousness - those who hear it not with such a believing and obedient mind and heart as they ought, but, instead of this (it may be) live in contrary practices, showing themselves stubborn and disobedient, and to every good work reprobate. Rebuke with all authority, as coming in the name of God, and armed with his threatenings and discipline, whoever make light of which will do it at their peril. Ministers are reprovers in the gate.

Quoted verse:
2 Timothy 3:16 [see Lesson]
All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:

III. Here is a special instruction to Titus in reference to himself: “Let no man despise thee; that is, give no occasion to do so, nor suffer it without reproof, considering that he who despiseth despiseth not man, but God.” Or thus, “Speak and exhort these things, press them upon all, as they may respectively be concerned; with boldness and faithfulness reprove sin, and carefully look to thyself and thy own conduct, and then none will despise thee.” The most effectual way for ministers to secure themselves from contempt is to keep close to the doctrine of Christ, and imitate his example - to preach and live well, and do their duty with prudence and courage; this will best preserve both their reputation and their comfort.

Perhaps too an admonition might be here intended to the people - that Titus, though young, and but a substitute of the apostle, yet should not be condemned by them, but considered and respected as a faithful minister of Christ, and encouraged and supported in his work and office. “Know those that labour among you, and are over you in the Lord, and admonish you; and esteem them very highly in love for their work's sake, 1 Thessalonians 5:12-13. Mind their teaching, respect their persons, support them in their function, and, what in you lies, further their endeavours for the honour of God and the salvation of souls.” ~Matthew Henry

Quoted verse
1 Thessalonians 5:12-13
12 And we beseech you, brethren, to know them which labour among you, and are over you in the Lord, and admonish you;
13 And to esteem them very highly in love for their work's sake. And be at peace among yourselves.

Now the Matthew Henry Concise. This commentary covers the rest of Chapter 2, verses 11-15.
 
The doctrine of grace and salvation by the gospel, is for all ranks and conditions of men. It teaches to forsake sin; to have no more to do with it. An earthly, sensual conversation suits not a heavenly calling. It teaches to make conscience of that which is good. We must look to God in Christ, as the object of our hope and worship. A gospel conversation must be a godly conversation. See our duty in a very few words; denying ungodliness and worldly lusts, living soberly, righteously, and godly, notwithstanding all snares, temptations, corrupt examples, ill-usage, and what remains of sin in the believer's heart, with all their hindrances. It teaches to look for the glories of another world. At, and in, the glorious appearing of Christ, the blessed hope of Christians will be complete: To bring us to holiness and happiness was the end of Christ's death. Jesus Christ, that great God and our Saviour, who saves not only as God, much less as Man alone; but as God-man, two natures in one person. He loved us, and gave himself for us; and what can we do less than love and give up ourselves to him! Redemption from sin and sanctification of the nature go together, and make a peculiar people unto God, free from guilt and condemnation, and purified by the Holy Spirit. All Scripture is profitable. Here is what will furnish for all parts of duty, and the right discharge of them. Let us inquire whether our whole dependence is placed upon that grace which saves the lost, pardons the guilty, and sanctifies the unclean. And the further we are removed from boasting of fancied good works, or trusting in them, so that we glory in Christ alone, the more zealous shall we be to abound in real good works. ~Matthew Henry Concise

Here are some things from the Biblical Illustrator:

Hints to ministers
The Christian teacher should always act with mildness, yet with firmness. There are gradations [grey-dey-shuh ns]* to be observed.
1. Instruction: “these things speak.”
2. Expostulation: “exhort.” [to urge, advise, or caution earnestly; admonish urgently.]
3. Reproof: Rebuke with authority. [Reproof: the act of reproving, censuring, or rebuking.] [Censure: strong or vehement expression of disapproval] ~Biblical Illustrator

*"Gradation" means any process or change taking place through a series of stages, by degrees, or in a gradual manner.

Despising the preacher
1. Men will despise a preacher when his life and his doctrine do not agree.
2. When he delivers his message with half-heartedness, as one who does not really believe it himself.
3. When it is evident he has bestowed no pains or labour on preparation for his work.
4. When by his manner he makes it plain that he desires to give prominence to himself, and excite admiration.
5. When he is evidently influenced by other motives than God’s glory and man’s good. ~Biblical Illustrator

Lessons
1. Let no man despising thee prevent the full discharge of certain duty. “He that despiseth you, despiseth Me, and he that despiseth Me, despiseth Him that sent Me.”
2. If men will despise God and Christ, the human messenger may well consent to be despised along with them. Let them despise thee, but let not the effect be caused by cowardly suppression, or disingenuous corruption of the truth on your part. As a faithful messenger of God and an ambassador of Christ, let men despise you if they will, or if they must—let them despise you at their peril. But as a traitor to the truth and to its Author, let no man despise thee. ~Biblical Illustrator

A summary of the “things” Titus was to “speak”
1. The central idea of the passage appears to be a life of sobriety, righteousness, and godliness, issuing in and sustaining the practical advice previously offered to old men and maidens, to matrons, aged and young, to youths, and slaves of all degrees.

2. The subjective condition of this heavenly life on earth is explicitly stated—a denial of all godlessness and worldly passions.

3. This “life” and its “conditions” are originated and promoted by a process of Divine discipline. Here are processes, mental and disciplinary, which augment and stimulate this life of godliness.

4. This entire subjective process rests upon two groups of sublime objective realities:
(1) The historic epiphany of the grace of God in the Incarnation;
(2) the anticipated and prophetic epiphany of the glory of our great God and Saviour Jesus Christ. Thus it calls for the exercise of the twofold energy of “faith” and “hope.”

5. The “grace” and the “glory of God,” received and appropriated in Christian faith and hope, attain their highest expression in the redemptive self-sacrifice of the God-man.

6. By way of closing the circle of the thought, it is expressly stated that the end of the redemptive work is the creation of “a holy people,” who are not only His “peculiar treasure” and inheritance, but who have, as the law and charter of their incorporation, this grand distinction, that they are charged with the genius of goodness—the passion for godliness. They are the very “zealots of goodness,” passionately eager for all that will help and move them to realize the ideal of the Divine life. ~Biblical Illustrator

Now to the specific commentaries.

We will go with the verse being in three parts. Some commentaries take on single words.

1] These things speak and exhort.
2] And rebuke with all authority.
3] Let no man despise thee

1] These things speak and exhort.

These things speak - That is, teach; for speak, has the same meaning here as teach, which, as being synonymous, is actually the reading of the Codex Alexandrinus. ~Adam Clarke

And exhort - Repeat them again and again, and urge them on their attention and consciences. ~Adam Clarke

These things speak and exhort - Sound doctrine, the doctrine of grace, the doctrines of salvation and redemption by Christ, of peace, pardon, and cleansing by his blood; these speak out clearly, plainly, publicly, boldly, and faithfully: and the things which become sound doctrine; the duties of religion suitable to every age and sex, a denying of ungodliness and worldly lusts, a sober, righteous, and godly life and conversation, exhort unto; and encourage the saints to be zealous of good works, and comfort them with the expectation of the blessed hope, and glorious appearance of Christ. ~John Gill

2] And rebuke with all authority.

And rebuke with all authority - The word “authority” here means command. The sense here is, he was to do it decidedly, without ambiguity, without compromise, and without keeping anything back. He was to state these things not as being advice or counsel, but as the requirement of God. ~Barnes Notes

And rebuke - Demonstrate the importance, utility, and necessity of them; and show them that God requires their obedience. ~Adam Clarke

With all authority - With all that authority with which thy office invests thee, and which thou hast received from God. ~Adam Clarke

And rebuke with all authority - such as imbibe errors and heresies, or indulge to vice and wickedness, with the authority both of Christ and his church, in the name of the one, and by the order and vote of the other, that the reproof may come with the greater weight; and in a grave and solemn manner, suitable to the dignity of the ministerial office and character, and with that sharpness and severity the offence requires. ~John Gill

3] Let no man despise thee

Let no man despise thee - That is, conduct yourself, as you may easily do, so as to command universal respect as a minister of God; see the notes at 1 Timothy 4:12.

Quoted verse:
1 Timothy 4:12 [see Lesson]
Let no man despise thy youth; but be thou an example of the believers, in word, in conversation, in charity, in spirit, in faith, in purity.

Let no man despise thee - That is: Act so that no person shall have any cause to despise thee, either for thy work, or the manner and spirit is which thou dost perform it.

Few portions of the New Testament excel this chapter. It may well form the creed, system of ethics, and text book of every Christian preacher. Does any man inquire what is the duty of a Gospel minister! Send him to the second chapter of the Epistle to Titus for a complete answer. There he will find what he is to believe, what he is to practice, and what he is to preach. Even his congregation is parceled out to him. The old and the young of both sexes, and those who are in their employment, are considered to be the objects of his ministry; and a plan of teaching, in reference to those different descriptions of society, is laid down before him. He finds here the doctrine which he is to preach to them, the duties which he is required to inculcate, the motives by which his exhortations are to be strengthened, and the end which both he and his people should have invariably in view. ~Adam Clarke

Let no man despise thee - as negligent in the discharge of his office, or as doing it in a pusillanimous [pyoo-suh-lan-uh-muh s] [lacking courage or resolution; cowardly; faint-hearted; timid.] manner, or as behaving in his life and conversation unworthy of the character he bore, and so is a direction to himself; or else it may be considered as designed for the churches in Crete, and the professors of religion, and to be an instruction to them to value Titus, and treat him with respect, and not with contempt; which shows that this epistle was not written for Titus only, or for his own use, but for the service of others. The Ethiopic version reads, "let no man deceive thee". ~John Gill

A Key statement recap:

Paul speaks directly to Titus:

--Proclaim the gospel message.
--Encourage the people as you show them their sins.
--Have conviction.

--Ministers must be in close adherence to scripture.
--Ministers must not be cold and lifeless in delivering heavenly doctrine and precepts.
--Ministers must call upon persons to mind and heed, and not be hearers only, deceiving themselves; but doers of the word, that they may be blessed therein

--Ministers are reprovers in the gate.
--Let no man despise thee; that is, give no occasion to do so, nor suffer it without reproof.
--With boldness and faithfulness reprove sin, and carefully look to thyself and thy own conduct, and then none will despise thee.

--The doctrine of grace and salvation by the gospel, is for all ranks and conditions of men.
--We must look to God in Christ, as the object of our hope and worship.
--And the further we are removed from boasting of fancied good works, or trusting in them, so that we glory in Christ alone, the more zealous shall we be to abound in real good works.

--The Christian teacher should always act with mildness, yet with firmness.
--Let no man despising thee prevent the full discharge of certain duty.
--Be a life of sobriety, righteousness, and godliness.

--This “life” and its “conditions” are originated and promoted by a process of Divine discipline.
--Repeat [the gospel] again and again, and urge them on their attention and consciences.
--Ministers speak sound doctrine, the doctrine of grace, the doctrines of salvation and redemption by Christ.

--Demonstrate the importance, utility, and necessity of [the requirements of God]; and show them that God requires their obedience.
--And rebuke with all authority - such as imbibe errors and heresies, or indulge to vice and wickedness.
--Does any man inquire what is the duty of a Gospel minister! Send him to the second chapter of the Epistle to Titus for a complete answer. There he will find what he is to believe, what he is to practice, and what he is to preach.

These are the lessons to Titus and all of us from verse 15.