Walking on water is an iconic, superhero thing to do. In a mighty display of divine power, Jesus strolls across the Sea of Galilee and then stills a strong wind. No wonder the disciples are terrified by the ghostly apparition coming toward them. Ghosts, after all, are spirits without flesh-and-blood bodies.
I had a classmate at an evangelical Christian college who repeatedly defined faith as “stepping out of airplanes, knowing that God will catch you.” My response was that surely God had better things to do than catch folks stupid enough to step out of airplanes. Matthew’s story of Jesus walking on the water with Peter can spawn bad theologies.