When Jesus walked on the water he wanted to stimulate faith of his disciples demonstrating that he is the Lord of natural forces. In the gospel of Matthew we read that disciples “were terrified, and said, “It is a ghost!” and they cried out in fear” (cf. Matthew chap. 14, verse 26). Ideed only a ghost is able to walk on the sea without sinking! But Jesus is not a ghost, because he reassures his disciples: “Take heart, It is I, do not be afraid” (cf. Matthew chap.14, verse 27).
Biblical world’s view is very different from our scientific view of the world. Ancient hebrews believed that seas and rivers were inhabited by monsters and ghosts; indeed disciples believed that the man walking on the water was not Jesus but a ghost. The question is: why Jesus walked on the sea? Disciples would answer saying “Jesus walked on the sea because he was the Son of God” (cf. Matthew chap. 14, verse 33). Nowadays we answer saying that the Matthew used a literary genre to describe not an historical fact, but to demonstrate the Jesus was God. The difference is that disciples believed that Jesus could walk on the sea because he was God. Today we don’t believe that Jesus really walked on the rough water, because Matthew don’t describe a fact but he want to give a message: Jesus is God and he don’t give up distressed disciples who believe in him.
Nowadays nobody ask himself if Jesus body was different from human body. For us it is impossible that an human body may walk on a liquid surface and that’s all! Is it not possible to assume that body of Jesus was transformed as in the Transfiguration? (cf. Matthew chap. 17) So Jesus that walks on the water wouldn’t be a ghost, but a transparent body lighter than water … in the post resurrection apparitions Jesus appears to the disceples who also believed he was a ghost (cf. Luke chap. 24, verses 34-37) but Jesus said them he wasn’t a ghost because they could touch him. In this case Jesus body wasn’t transparent but also able to get through locked doors! So the problem remains: what was the body of Jesus?