John Calvin Commentary Acts 14:26

"and thence they sailed to Antioch, from whence they had been committed to the grace of God for the work which they had fulfilled." — Acts 14:26 (ASV)

When they had been commended. Luke might have said that they were ordained there to be the apostles of the Gentiles. However, using an indirect expression, he more plainly conveys that they were neither sent away by men nor did they attempt anything trusting in their own strength, but rather that their whole journey, along with its success, was committed to God, its author.

Therefore, their preaching was not man’s work, but a work of the grace of God.

And the word grace refers both to the power and efficacy of the Spirit and to all other signs of favor, because all those gifts that God bestows upon his servants are free.

And the meaning of this phrase can be understood as follows: they prayed God that he would manifest his grace to further the labors of his servants.