Matthew 14:28

And Peter answered him and said
Who knew his voice, and was ready to believe it might be Christ; and having more courage, and being more forward than the rest of the disciples, ventured to speak to him; saying,

Lord, if it be thou;
for he was not fully assured that it was he: he might consider that nocturnal apparitions are deceitful, and that Satan can transform himself into an angel of light, and could put on the appearance, and mimic the voice of Christ; wherefore, to try whether it was a spectre, or really Christ, he says,

bid me come unto thee on the water;
thereby expressing great love and affection to Christ, being willing to come to him, though through danger, through storms and tempests; and also his strong faith in him, supposing it to be he; who, he knew, was as able to support his body on the water, as his own; and yet much modesty, submission, and dependence; not willing to take a step without his order.