John Calvin Commentary 1 John 5:11

"And the witness is this, that God gave unto us eternal life, and this life is in his Son." — 1 John 5:11 (ASV)

That God hath given us eternal life. Having now set forth the benefit, He invites us to believe. It is, indeed, a reverence due to God, to immediately receive, as beyond controversy, whatever He declares to us. But since He freely offers life to us, our ingratitude will be intolerable, unless with prompt faith we receive a doctrine so sweet and so lovely. And, doubtless, the words of the Apostle are intended to show that we ought not only reverently to obey the gospel, lest we should affront God, but also that we ought to love it, because it brings to us eternal life. From this we also learn what is especially to be sought in the gospel, namely, the free gift of salvation; for God's exhortation to us there to repentance and fear ought not to be separated from the grace of Christ.

But the Apostle, so that he might keep us together in Christ, again repeats that life is found in Him, as if he had said that no other way of obtaining life has been appointed for us by God the Father.

And the Apostle, indeed, briefly includes here three things:

1. That we are all given up to death until God in His gratuitous favor restores us to life (for He plainly declares that life is a gift from God, and from this it also follows that we are destitute of it and that it cannot be acquired by merits).
2. He teaches that this life is conferred on us by the gospel, because in it the goodness and paternal love of God are made known to us.
3. He says that we cannot become partakers of this life otherwise than by believing in Christ.