So, in the course of their travels, Jesus sent the disciples on ahead of him to Bethsaida, a journey they made by taking a boat across the Sea of Galilee. A storm blew up, and the disciples were in fear of their lives before Jesus walked across the surface of the lake, supported by nothing more than water (and the ineffable power of the God of Israel). Tthe disciples were understandably discombobulated by this apparent apparition, but then Jesus climbed into the boat himself, proving that he was real.
In what is something of a common theme for Simon Peter – although this time mentioned only in Matthew – the future first Pope started off with good intentions but lost faith quickly. He walked out onto the water towards Jesus, but then became afraid, and began to sink. Jesus pulled him from the water and they both walked back to the boat.