19 If ye were of the world, the world would love his own: but because ye are not of the world, but I have chosen you out of the world, therefore the world hateth you.
[AD 407] John Chrysostom on John 15:17-21
(Hom. lxxvii. 2) Or thus: I have said that I lay down My life for you, and that I first chose you. I have said this not by way of reproach, but to induce you to love one another. Then as they were about to suffer persecution and reproach, He bids them not to grieve, but rejoice on that account: If the world hate you, ye know that it hated Me before it hated you: as if to say, I know it is a hard trial, but ye will endure it for My sake.

(Hom. lxxvii. 2) As if Christ's suffering were not consolation enough, He consoles them still further by telling them, the hatred of the world would be an evidence of their goodness; so that they ought rather to grieve if they were loved by the world: as that would be evidence of their wickedness.

As if He said, Ye must not be disturbed at having to share My sufferings; for ye are not better than I.

(Hom. lxxvii. 2) Then follows another consolation, viz. that the Father is despised and injured with them: But all these things will they do unto you for My name's sake, because they know not Him that sent Me.

[AD 430] Augustine of Hippo on John 15:17-21
(Tract. lxxxvii. 1) Our Lord had said, I have ordained that ye should walk, and bring forth fruit. Love is this fruit. Wherefore He proceeds: These things I command you, that ye love one another. (Gal. 5:22) Hence the Apostle saith: The fruit of the Spirit is love; and enumerates all other graces as springing from this source. Well then doth our Lord commend love, as if it were the only thing commanded: seeing that without it nothing can profit, with it nothing be wanting, whereby a man is made good.

(Tract. lxxxvii. 2) For why should the members exalt themselves above the head? Thou refusest to be in the body, if thou art not willing, with the head, to endure the hatred of the world. For love's sake let us be patient: the world must hate us, whom it sees hate whatever it loves; If ye were of the world, the world would love his own.

(Tract. lxxxvii. 2) He saith this to the whole Church, which is often called the world; as, God was in Christ, reconciling the world unto Himself. (2 Cor. 5:19) The whole world then is the Church, and the whole world hateth the Church. The world hateth the world, the world in enmity, the world reconciled, the defiled world, the changed world. (Tract. lxxxviii. 4.). Here it may be asked, If the wicked can be said to persecute the wicked; e. g. if impious kings, and judges, who persecute the righteous, punish murderers and adulterers also; how are we to understand our Lord's words, If ye were of the world, the world would love his own? In this way; The world is in them who punish these offences, and the world is in them who love them. The world then hates its own so far as it punishes the wicked, loves its own so far as it favours them. (Tract. lxxxvii. 4.). Again, if it be asked how the world loves itself, when it hates the means of its redemption, the answer is, that it loves itself with a false, not a true love, loves what hurts it; hates nature, loves vice. Wherefore we are forbidden to love what it loves in itself; commanded to love what it hates in itself. The vice in it we are forbidden, the nature in it we are commanded, to love. And to separate us from this lost world, we are chosen out of it, not by merit of our own, for we had no merits to begin with, not by nature which was radically corrupt, but by grace: But because ye are not of the world, but I have chosen you out of the world, therefore the world hateth you.

(Tract. lxxxviii. 1) Our Lord, in exhorting His servants to bear patiently the hatred of the world, proposes to them an example than which there can be no better and higher one, viz. Himself: Remember the word that I said unto you, The servant is not greater than his lord. If they have persecuted Me, they will also persecute you: if they have kept My saying, they will keep yours also.

(Tract. lxxxviii. 1) The servant is not greater than his Lord. Here the servant is the one who has the purified fear, which abideth for ever.

(Tract. lxxxviii. 2) All these things, viz. what He had mentioned, that the world would hate them, persecute them, despise their word. For My Name's sake, i. e. in you they will hate Me, in you persecute Me, your word they will not keep, because it is mine. They who do these things for His name's sake are as miserable, as they who suffer them are blessed: except when they do them to the wicked as well; for then both they who do, and they who suffer, are miserable. But how do they do all these things for His name's sake, when they do nothing for Christ's name's sake, i. e. for justice sake? We shall do away with this difficulty, if we take the words as applying to the righteous; as if it were, All these things will ye suffer from them, for My name's sake. If, for My name's sake, mean this, i. e. My name which they hate in you, justice which they hate in you; of the good, when they persecute the wicked, it may be said in the same way, that they do so both for righteousness' sake, which they love, which love is their motive in persecuting, and for unrighteousness' sake, the unrighteousness of the wicked, which they hate. Because they know not Him that sent Me, i. e. know not according to that knowledge of which it is said, To know Thee is perfect righteousness. (Wisd. 15:3)

[AD 604] Gregory the Dialogist on John 15:17-21
(Hom. in Ezech. ix.) For the dispraise of the perverse, is our praise. There is nothing wrong in not pleasing those, who do not please God. For no one can by one and the same act please God, and the enemies of God. He proves himself no friend to God, who pleases His enemy; and he whose soul is in subjection to the Truth, will have to contend with the enemies of that Truth.

[AD 1107] Theophylact of Ohrid on John 15:17-21
Or thus: If, Me says, they have persecuted your Lord, much more will they persecute you; if they had persecuted Him, but kept His commandments, they would keep yours also.

[AD 1274] Glossa Ordinaria on John 15:17-21
They observed1 it in order to calumniate it, as we read in the Psalms, The ungodly seeth2 the righteous.

[AD 397] Ambrose of Milan on John 15:19
That which is promised to us is already present with you, and the object of your prayers is with you. You are of this world and yet not in this world. This age has held you but has not been able to retain you.

[AD 407] John Chrysostom on John 15:19
So that had ye been loved it would be very clear that you had shown forth signs of wickedness. Then, when by saying this first, He did not effect his purpose, He goes on again with the discourse.
[AD 444] Cyril of Alexandria on John 15:19
He lightens by His art even that which was most grievous, and gives them unexpected pleasure at that which it was reasonable to suppose would greatly trouble them. For to be hated by any is truly burdensome, because sly injuries and unexpected devices are the result; yet this too is sweet when it happens for the sake of God and righteousness, and it supplies a convincing proof that the man against whom some thus act is not of the world. For as we find physical so also shall we find moral affinities, and a sameness and complete likeness of disposition is sufficient to undermine mere blood-relationship.

For every creature loveth its like, according to the Scripture, and a man will be attached to his like. Now whereas similarity of character renews the law of love towards one another, the holy will live with the holy and very readily conform to him, and be joined to him in friendly union. And so also will be the attitude of one of like disposition towards a blasphemer. For this reason the Mosaic Law made a complete distinction between what was holy and profane, keeping such things apart and separate from one another according to the law of love.

Evil company doth corrupt good manners, and differences of disposition are at war with one another, and wills that are divided look in opposite directions and almost accuse one another: each being enamoured of its own pursuit. The lover of virtue then must incur hatred for the very things which excite our admiration----his rebuking vice and unveiling the vileness of the wicked by the contrast that his own manner of life presents. For when goodness is seen by its side, what is evil must appear unseemly. For this cause then I think those who are not enamoured of the same manner of life rage against the virtuous.

He bids then His disciples not be pained, even though they see themselves hateful to the world on account of their love of virtue and righteousness towards Him, but explains that they ought on the contrary to rejoice, receiving the hatred of the world as a proof of their dignity and praise with God. For see how dangerous He has shown their not enduring to suffer (which it was likely they would prefer) to be. For to be hated by any was not absolutely without loss. But it has not the free pardon from God, and the great gain which results from preferring to suffer it. For if the man who is hated by those who mind worldly things is considered as outside the world, it is necessary then to suppose that the man who is not hated is united to the vices of the world.

What then has Christ established by these words? That they should preach His word with boldness, and should not permit their hearers to be unprofited, from their regard towards sinners or those who prefer to disobey the Divine command; but that, leaving unnoticed the affronts that will often result from being hated, they should give bold and fearless counsel, passing by nothing whatsoever or esteeming anything of more consequence than the necessity of serving God. This object St. Paul well accomplishes when he writes thus: For am I now persuading mien, or God? or am I seeking to please men? If I were still pleasing men, I should not be a servant of Christ. For it is not possible to please evil men and God. For how could the two coincide, the will of each presenting the widest divergence? For one looks towards virtue, and the other looks towards vice. The man therefore who wishes only to be the servant of God, and who regards nothing as superior to piety towards Him, must necessarily be in conflict with those who love the world, whenever he persuades them to a state of mind out of harmony with the vain folly of the world. For advice which calls to something else is most intolerable to lovers of pleasure, as assuredly are profitable and severe remedies to those whose bodies are diseased by these passions.
[AD 604] Gregory the Dialogist on John 15:19
For the disparaging of the perverse [toward us] is our praise. There is nothing wrong in not pleasing those who do not please God. For no one can by one and the same act please God and the enemies of God. He proves himself no friend to God who pleases his enemy. And he whose soul is in subjection to the Truth will have to contend with the enemies of that Truth.