1 John 3:1

"For the world knows us not, as it knew Him not." He means by the world those who live a worldly life in pleasures.

"But," say they, "God is `good, 'and `most good, ' and `pitiful-hearted, 'and `a pitier, 'and `abundant in pitiful-heartedness, ' which He holds `dearer than all sacrifice, ' `not thinking the sinner's death of so much worth as his repentance', `a Saviour of all men, most of all of believers.' And so it will be becoming for `the sons of God' too to be `pitiful-hearted' and `peacemakers; ' `giving in their turn just as Christ withal hath given to us; ' `not judging, that we be not judged.' For `to his own lord a man standeth or falleth; who art thou, to judge another's servant? ' `Remit, and remission shall be made to thee.'"

In Cicero, Catulus in the Hortensius, while he prefers philosophy to all things, says that he would rather have one short treatise respecting duty, than a long speech in behalf of a seditious man Cornelius. And this is plainly to be regarded not as the opinion of Catulus, who perhaps did not utter this saying, but as that of Cicero, who wrote it. I believe that he wrote it for the purpose of recommending these books which he was about to write on Offices, in which books he testifies that nothing in the whole range of philosophy is better and more profitable than to give precepts for living. But if this is done by those who do not know the truth, how much more ought we to do it, who are able to give true precepts, being taught and enlightened by God?

"Behold what manner of love the Father hath given us, that we should be called sons of God, and be (such)." For whoso are called sons, and are not sons, what profiteth them the name where the thing is not? How many are called physicians, who know not how to heal! how many are called watchers, who sleep all night long! So, many are called Christians, and yet in deeds are not found such; because they are not this which they are called, that is, in life, in manners, in faith, in hope, in charity. But what have ye heard here, brethren? "Behold, what manner of love the Father hath bestowed upon us, that we should be called, and should be, the sons of God: therefore the world knoweth us not, because it hath not known Him, us also the world knoweth not." There is a whole world Christian, and a whole world ungodly; because throughout the whole world there are ungodly, and throughout the whole world there are godly: those know not these. In what sense, think we, do they not know them? They deride them that live good lives. Mark well and see: for haply there are such also among you. Each one of you who now lives godly, who despises worldly things, who does not choose to go to spectacles, who does not choose to make himself drunken as it were by solemn custom, yea, what is worse, under countenance of holy days to make himself unclean: the man who does not choose to do these things, how is he derided by those who do them! Would he be scoffed at if he were known? But why is he not known? "The world knoweth Him not." Who is "the world"? Those inhabiters of the world. Just as we say, "a house;" meaning, its inhabitants. These things have been said to you again and again, and we forbear to repeat them to your disgust. By this time, when ye hear the word "world," in a bad signification, ye know that ye must understand it to mean only lovers of the world because through love they inhabit, and by inhabiting have become entitled to the name. Therefore the world hath not known us, because it hath not known Him. He walked here Himself, the Lord Jesus Christ in the flesh; He was God, He was latent in weakness. And wherefore was He not known? Because He reproved all sins in men. They, through loving the delights of sins, did not acknowledge the God: through loving that which the fever prompted, they did wrong to the Physician.

God shows us the necessary patience because of the inheritance which he has given us. Here the “world” refers to wicked people.

For this reason, the world does not know us, because it did not know Him. In this place, he calls the lovers of the world. And this is what the same will say in judgment, seeing the glory of the saints whose faith they despised, they will say within themselves, groaning and repenting: These are they whom we once had in derision, and in a likeness of a reproach. We fools considered their life to be madness, and their end without honor. How are they counted among the children of God, and their lot among the saints (Wisdom V)?

See what kind of love the Father has given us, that we should be called children of God. For this reason the world does not know us, because it did not know Him. Beloved, we are now children of God, and it has not yet appeared what we shall be. But we know that when He appears, we shall be like Him; for we shall see Him as He is. And everyone who has this hope in Him purifies himself just as He is pure.
After John spoke about the assembly of antichrists and their perverse doctrine, by which they have made themselves revealed as if by a certain mark [χαρακτηρί]: and he sufficiently strengthened them, so that they would persist immovably in those things in which they had been instructed, he then adds the reward also set aside because of these things, making them stronger through the clarity of the rewards, and says: "abide in Him." (1 Jn. 2:27) Why? “So that when He appears we may have confidence.” (1 Jn. 2:28) For what is clearer or more desirable than the confidence with which we will present our labors completed in life to Christ, doing this with confidence and not experiencing shame at his coming? And since it was likely that some would ask by what works they could become pleasing to Him, John teaches this also and says: If you know that He is righteous, you know that everyone who practices righteousness is born of Him: (1 Jn. 2:29) for the righteous produces righteous ones. Furthermore, no one is unaware of how this relates to our glory and confidence: just as no one is ignorant of the greatness and quality of the love and kindness he has shown towards you.
For see what he has given us, that we should be called his children. And if this is hidden from those who are in the world, that we are the children of God, do not marvel at this: for this reason the world does not know us, because it did not know Him who adopted us as children. That the world is called a chaotic multitude, we have demonstrated in many places. Then, after John confirmed the adoption, he clearly says after this the glory and confidence or freedom that is reserved for those who have been adopted, and he says:
"Beloved, now we are children of God." But if he were to say: Indeed, Beloved, from the preceding you know that we are adopted as children of God: and if this has not yet been revealed, do not be troubled: for what is now uncertain will be revealed when He is revealed. Indeed, we will display the glory of adoption appearing as His likeness; for children are altogether like their father.
But having confidence toward Him as children, we shall see Him as He is: not certainly according to His nature; for this is impossible for created nature: but what? the righteous of the righteous, the pure of the pure. For like follows the like. For this reason, I said a little earlier that we shall be like Him: not according to nature; for otherwise He would have said not "like," but "the same," but now because this will not happen, He said "like," according to the quality of glory, indeed. It should be noted, however, that he did not say previously, "Everyone who has done or will do righteousness," but "He who does." For virtues always operate: and while they are being done, they have being; but those that cease or are to come, do not even have being.