John Calvin Commentary Acts 16:31

"And they said, Believe on the Lord Jesus, and thou shalt be saved, thou and thy house." — Acts 16:31 (ASV)

Believe in the Lord Jesus. This is but a short, and, at first glance, a seemingly cold and unsatisfying definition of salvation, and yet, to believe in Christ is complete. For Christ alone has all the components of blessedness and eternal life included in Him, which He offers to us by the gospel; and by faith we receive them, as I have declared (Acts 15:9). And here we must note two things: first, that Christ is the target at which faith must aim; and, therefore, people's minds do nothing but wander when they turn aside from Him.

Therefore, it is no wonder if all the theology of Popery is nothing else but a huge mass and horrible labyrinth, because, neglecting Christ, they flatter themselves with vain and frivolous speculations. Secondly, we must note that after we have embraced Christ by faith, that alone is sufficient for salvation. But the subsequent statement, which Luke adds, better expresses the nature of faith: Paul and Silas command the keeper of the prison to believe in the Son of God.

Do they limit themselves precisely to this statement alone? Indeed, it follows in Luke’s text that they preached the word of the Lord. Therefore, we see how faith is not a slight or dry opinion about unknown things, but a clear and distinct knowledge of Christ, understood from the gospel.

Again, if the preaching of the gospel is absent, faith will no longer remain. To conclude, Luke connects faith with preaching and doctrine; and after he has briefly spoken of faith, he, by way of exposition, shows the true and proper way of believing. Therefore, instead of that fabrication of entangled faith, about which the Papists babble, let us hold to faith revealed in the Word of God, so that it may reveal to us the power of Christ.