I need now to say something about the meaning of the Lord’s “taking up sins” [John 1:29]. His “taking up sins” means much the same as his redeeming us and saving us, since the Lord came into the world so that we could be saved; if he had not come no one could have been reformed and reborn and therefore saved. This could happen, though, after the Lord had taken all power away from the Devil—that is, from hell—and had glorified his human nature—that is, united it to the divine nature of his Father. If these things had not happened, no human beings could have accepted anything divinely true that dwelt within them, let alone anything divinely good, because the Devil, who had had the greater power before these events, would have snatched it from their hearts.
We can see from all this that the Lord did not take away sins by his suffering on the cross, but that he does take away sins—that is, lay them aside—in those who believe in him and live by his commandments. This is what the Lord is telling us in Matthew:
Do not think that I have come to destroy the Law and the Prophets. Whoever breaks the least of these commandments and teaches others to do the same will be called the least in the kingdom of the heavens; but whoever does and teaches [these commandments] will be called great in the kingdom of the heavens. (Matthew 5:17, 19)
Reason alone should convince anyone who is the least bit enlightened that sins can be taken away from us only by active repentance—that is, by our seeing our sins, begging the Lord for help, and desisting from them. To see and believe and teach anything else does not come from the Word or from sound reason but from the desire and ill intent that come from our own sense of self-importance—an attitude that corrupts our understanding.
from The Lord, Section 17