John Calvin Commentary 1 John 5:19

"We know that we are of God, and the whole world lieth in the evil one." — 1 John 5:19 (ASV)

We are of God. He derives an exhortation from his previous teaching. For what he had declared generally concerning God's children, he now applies to those to whom he was writing. His purpose in this was to urge them to beware of sin and to encourage them to resist Satan's attacks.

Readers should observe that only true faith applies God's grace to us, so to speak; for the Apostle acknowledges no one as faithful except those who have the dignity of being God’s children. Nor indeed does he substitute probable conjecture (as the Sophists call it) for confidence; for he says that we know. The meaning is that, since we have been born of God, we ought to strive to prove by our separation from the world and by the sanctity of our life that we have not been called in vain to such great honor.

Now, this is a very necessary admonition for all the godly. For wherever they turn their eyes, Satan has his allurements prepared, by which he seeks to draw them away from God. It would then be difficult for them to continue in their course if they did not value their calling enough to disregard all the world's hindrances. Therefore, to be well prepared for the contest, these two things must be kept in mind: that the world is wicked, and that our calling is from God.

Under the term world, the Apostle no doubt includes the whole human race. By saying that it lieth in the wicked one, he represents it as being under the dominion of Satan.

Therefore, there is no reason why we should hesitate to shun the world, which condemns God and delivers itself into Satan's bondage. Nor should we fear its enmity, because it is alienated from God.

In short, since corruption pervades all nature, the faithful ought to practice self-denial. And since nothing is seen in the world but wickedness and corruption, they must necessarily disregard flesh and blood so that they may follow God.

At the same time, this other truth ought to be added: God is the one who has called them, so that under His protection they may oppose all the machinations of the world and Satan.