John Calvin Commentary 1 John 5:18

"We know that whosoever is begotten of God sinneth not; but he that was begotten of God keepeth himself, and the evil one toucheth him not." — 1 John 5:18 (ASV)

We know that whoever is born of God—if you suppose that God’s children are completely pure and free from all sin, as the fanatics contend, then the Apostle is inconsistent with himself, for he would thus take away the duty of mutual prayer among fellow believers. He then says that those sin not who do not completely fall away from the grace of God; therefore, he inferred that prayer should be made for all the children of God, because they do not sin unto death.

A proof is added: everyone born of God keeps himself—that is, keeps himself in the fear of God—and does not allow himself to be so led astray as to lose all sense of religion and surrender himself completely to the devil and the flesh.

For when he says that he is not touched by that wicked one, reference is made to a deadly wound; for the children of God do not remain untouched by the assaults of Satan, but they ward off his blows with the shield of faith, so that these do not penetrate the heart. Thus, spiritual life is never extinguished in them. This is not to sin. Though the faithful indeed fall through the weakness of the flesh, yet they groan under the burden of sin, loathe themselves, and do not cease to fear God.

Keeps himself. What properly belongs to God he transfers to us, for if any one of us were the keeper of his own salvation, it would be a miserable protection. Therefore, Christ asks the Father to keep us, intimating that this is not done by our own strength.

The advocates of freewill seize upon this expression so that they may prove from this that we are preserved from sin partly by God’s grace and partly by our own power. But they do not perceive that the faithful do not have from themselves the power of preservation of which the Apostle speaks.

Nor, indeed, does he speak of their power, as though they could keep themselves by their own strength; rather, he only shows that they should resist Satan, so that they may never be fatally wounded by his darts. And we know that we fight with no other weapons than those of God. Thus, the faithful keep themselves from sin to the extent that they are kept by God (John 17:11).