Albert Barnes Commentary 1 John 3:5

"And ye know that he was manifested to take away sins; and in him is no sin." — 1 John 3:5 (ASV)

And you know that he was manifested. The Lord Jesus, the Son of God. "You know that he became incarnate, or appeared among men, for the very purpose of putting an end to sin" (Matthew 1:21). (Compare to 1 Timothy 3:16).

This is the second argument in this paragraph (1 John 3:4–10), by which the apostle would deter us from sin. The argument is a clear one, and is perhaps the strongest that can be made to bear on the mind of a true Christian—that the Lord Jesus saw sin to be so great an evil, that he came into our world, and gave himself to the bitter sorrows of death on the cross, to redeem us from it.

To take away our sins. The essential argument here is that the whole work of Christ was designed to deliver us from the dominion of sin, not to furnish us the means of indulgence in it; and that, therefore, we should be deterred from it by all that Christ has done and suffered for us. He perverts the whole design of the coming of the Savior who supposes that his work was in any degree designed to procure for his followers the indulgences of sin, or who so interprets the methods of his grace as to suppose that it is now lawful for him to indulge his guilty passions. The argument essentially is this:

1. That we profess to be the followers of Christ, and should carry out his ends and views in coming into the world;
2. That the great and leading purpose of his coming was to set us free from the bondage of transgression;
3. That in doing this he gave himself up to a life of poverty, and shame, and sorrow, and to a most bitter death on the cross; and,
4. That we should not indulge in that from which he came to deliver us, and which cost him so much toil and such a death. How could we indulge in that which has brought heavy calamity on the head of a father, or which has pierced a sister's heart with many sorrows? Still more, how can we be so ungrateful and hardhearted as to indulge in that which crushed our Redeemer in death?

And in him is no sin. An additional consideration to show that we should be holy. As he was perfectly pure and spotless, so should all his followers aim to be; and none can truly pretend to be his who do not desire and design to become like him. On the personal holiness of the Lord Jesus, see Hebrews 7:26 and 1 Peter 2:23.