Peter - walked on the water - However impossible the thing commanded by Christ may appear, it is certain he will give power to accomplish it to those who receive his word by faith; but we must take care never to put Christ's power to the proof for the gratification of a vain curiosity; or even for the strengthening of our faith, when the ordinary means for doing that are within our reach.

And he said, come,.... This he said, partly to assure them who he was; for had he denied him, he and the rest might have concluded, it was none of Jesus; and partly to commend his love, and confirm his faith, by giving a further instance of his power, in enabling him to walk upon the water, as he did:
and when Peter was come down out of the ship; as he immediately did, having orders from Christ; and being by this second speech fully convinced it was he
he walked on the water; a little way, being supported and enabled by the power of Christ; for this was an extraordinary and miraculous action: for if it was so in Christ, it was much more so in Peter: Christ walked upon the water by his own power, as God; Peter walked upon the water, being held up by the power of Christ. The Jews (w) indeed, call swimming , "walking upon the face of the waters": hence we read of a swimmer's vessel, which is explained to be what men make to learn in it, how "to go or walk upon the face of the waters" (x); but then this is not going upon them upright, but prone, or lying along upon the surface of the waters, which was not Peter's case; he did not, as at another time, cast himself into the sea, and swim to Christ; see John 21:7 but as soon as he came down from the ship, standing upright, he walked upon the waters,
to go to Jesus; not merely for walking sake, but for the sake of Christ, he dearly loved; that he might be with him, and be still more confirmed of the truth of its being he, and not a spirit.
(w) R. David Kimchi, Sepher Shorash. rad. (x) R. Song. Urbin. Ohel moed, fol. 78. 1.

And he said, Come. And when Peter had come down out of the boat. he walked on the water, to go to Jesus--(Also see on Mark 6:50.)

And he said, Come. I suppose the Lord bade Peter to come in order to teach him a lesson.