John Calvin Commentary Acts 11:21

"And the hand of the Lord was with them: and a great number that believed turned unto the Lord." — Acts 11:21 (ASV)

The hand of the Lord was. Luke proves by the success that the gospel was offered to the Gentiles also by the brethren of Cyprus and Cyrene not rashly or without careful consideration, because their labor was fruitful and profitable. But such increase would never have followed unless God had commanded and favored.

Therefore, it follows that it pleased God that the Gentiles should be called. The hand, as is well known, signifies power and strength. Therefore, this is Luke’s meaning: that God testified by his present aid that the Gentiles were called together with the Jews, through his direction, to be made partakers of the grace of Christ.

And this blessing of God served significantly to confirm the minds of all men. This passage also teaches us that whatever pains the ministers of God take in teaching, it will all be vain and void unless God blesses their labors from heaven. For we may plant and water, as Paul teaches, but the increase comes from God alone (1 Corinthians 3), in whose hand the hearts of men are, that he may bend and shape them as he pleases.

Therefore, as often as we are to speak of faith, let us always remember this teaching: that God worked through his ministers, and that he made their doctrine effectual by his hand, that is, by the secret inspiration of the Spirit. Therefore, let the minister attempt nothing trusting in his own wisdom and effort, but let him commit his labor to the Lord, upon whose grace all success depends. And where doctrine works effectually, let those who believe thank God for their faith.

Furthermore, we must note what Luke says, that many were turned to God by faith, because he very well expresses the force and nature of faith: that it is not idle and cold, but such as restores men (who were before turned away from God) to his government and binds them to his righteousness.