John Calvin Commentary Acts 14:9

"The same heard Paul speaking, who, fastening eyes upon him, and seeing that he had faith to be made whole," — Acts 14:9 (ASV)

He heard Paul speak. Hearing is recorded first, so that we may know that the faith which Luke will subsequently commend came from Paul’s doctrine. Therefore, when he heard Paul, he hoped to be healed. But the question is, whether this was promised to him specifically, for God does not command us to hope for everything immediately when He offers us eternal salvation in the gospel.

I answer that this was a unique and extraordinary prompting of the Spirit of God in the cripple, as it was likewise in Paul, when he perceived his faith merely by looking at him. Many may receive the gospel, and yet they will not be cured of those diseases with which they are afflicted.

But since God was determined to show a sign of His grace in the cripple, He prepared his mind beforehand and made him capable of what was to come upon him. Therefore, we must not make this a common rule merely because the cripple believed he would be healed; rather, it was a special preparation to receive the gift of healing. And this kind of faith, which makes way for miracles, is also particular; many of God’s children lack it, who are, nevertheless, endowed with the Spirit of adoption.

Whom when Paul beheld steadfastly. We know how doubtful and deceitful a person's countenance is; therefore, no sure judgment concerning faith could be given by it, for faith has God alone as its witness. But, as I have already said, the cripple’s faith was revealed to Paul by the secret inspiration of the Spirit, just as the Spirit was the apostles' only guide and master for working miracles.