John Calvin Commentary Acts 11:23

"who, when he was come, and had seen the grace of God, was glad; and he exhorted them all, that with purpose of heart they would cleave unto the Lord:" — Acts 11:23 (ASV)

When he had seen the grace of God. By these words Luke teaches, first, that the gospel which they had received was true; secondly, that Barnabas sought nothing else but the glory of Christ. For, when he says that he saw the grace of God, and that he exhorted them to go forward, from this we gather that they were well taught. And the joy is a testimony of sincere godliness. Ambition is always envious and malicious, so that we see many seek praise by rebuking other men, because they are more desirous of their own glory than of the glory of Christ. But the faithful servants of Christ must rejoice (as Barnabas did) when they see the gospel increase, by whomever God shall make His name known. And certainly, those who help one another, acknowledging that all the effect that springs from it is the work of God, will never envy one another, nor will they seek to find fault with one another, but will, with one mouth and mind, praise the power of God.

Again, it is worth noting that Luke attributes the faith of the men of Antioch, and whatever was worthy of praise there, to the grace of God. He might have listed all those virtues that could contribute to the commendation of men, but he encompasses whatever excellence was in that Church under this word grace. Lastly, we must note Barnabas’ exhortation.

We have already said that Barnabas subscribed to the former doctrine which they had embraced; but to prevent doctrine from falling away, it is essential that it be thoroughly imprinted in the minds of the faithful by continual exhortations. For since we have to continually encounter so many strong adversaries, and our minds are so slippery, unless each person arms himself diligently, doctrine will soon fall away, as the falling away of countless individuals demonstrates.

Since he sets down this manner of perseverance—that they continue with purpose of heart—we are taught by this that faith has taken deep root when it has a place in the heart. Therefore, it is no wonder if scarcely one out of ten of those who profess faith stands firm to the end, since very few know what the affection and purpose of heart mean.