Theophylact of Ohrid

Showing that the cause of his sinking was not the wind but faintheartedness, Christ does not rebuke the wind, but the fainthearted Peter. This is why He raised him up and set him on the water, but allowed the wind to blow. Peter did not doubt in everything, but in part. Inasmuch as he was afraid, he showed lack of faith; but by crying out, "Lord, save me," he was healed of his unbelief. …

Commentary on Matthew ↗

Augustine of Hippo

While human praise does not tempt the Lord, people are often ruffled and nearly entranced by human praise and honors in the church. Peter was afraid on the sea, terrified by the great force of the storm. Indeed, who does not fear that voice: "Those who say you are happy place you in error and disturb the path of your feet"? And since the soul struggles against the desire for human praise, it is good for it to turn to prayer and petition amid such danger, lest one who is charmed by praise be overcome by criticism and reproach. …

Sermon 75.10 ↗

Jerome

And immediately Jesus, stretching out His hand, took hold of him and said to him, 'You of little faith, why did you doubt?' And when they got into the boat, the wind stopped. If it is said to the Apostle Peter, of whose faith and ardor of mind we have spoken above, who confidently asked the Savior, saying, 'Lord, if it is You, command me to come to You on the water,' because he was a little afraid, 'You of little faith, why did you doubt?' What must we say, who have even the smallest portion of this little faith?

Commentary on Matthew ↗

Thomas Aquinas

And immediately Jesus stretching forth his hand took hold of him. Christ does two things: he both gives help and rebukes his lack of faith. He gives help by extending his hand; Ps. 143:7: put forth your hand from on high, deliver me and rescue me from many waters. And Job 14:15: to the work of your hands you shall reach out your right hand. Then he rebukes him for his lack of faith, and says to him: O you of little faith, why did you doubt? …

Commentary on Matthew ↗