Jesus did a lot of miracles. We don't know how he did them. Jesus is God, so he can do anything. Walking on the water was not Jesus' ordinary way of getting around. He did this miracle, like other miracles, to teach his disciples and to show them his power. Jesus is Lord of the laws or the universe - he's in charge of the water, too, so he can walk on it whenever he wants to.
That evening his disciples went down to the shore to wait for him. Darkness fell and Jesus still hadn't come back. So they got into the boat and headed out across the lake toward Capernaum. But soon a storm swept down upon them as they rowed. The sea grew very rough. And they were in the middle of the lake. Suddenly they saw Jesus walking toward the boat! They were terriied. So he called out to them and told them not to be afraid. Then they were willing to let him come to them. And suddenly the boat was already at the place where they were going! (John 6:16-21)
Matthew 14:23-32; Mark 4:35-41; 6:45-51
Note to Parents
Lots of well-meaning people have tried to explain miracles (such as Jesus' walking on the water) to make them believeable to children. But this is a tragic mistake. The fact that miracles are incredible is exactly the point - they show us that God is awesome and powerful.