What does John 6:21 mean?
The gospel of John records seven specific miracles, described as signs: events carrying specific meaning, purpose, or message. In John's case, these are collected as evidence that Jesus Christ really is God incarnate. Two are recorded in this chapter alone: Christ feeding thousands (John 6:1–15) and Christ walking on the water (John 6:16–21). Here, however, there is another miracle described in an almost off-handed way.Mark chapter 6 and Matthew chapter 14 give the details which John leaves out of this account. The men crossed the Sea of Galilee at Jesus' directive (Mark 6:45), encountering high winds and rough seas. Jesus, however, is watching from the shore, and walks out to them sometime just before sunrise (Mark 6:48). Even though the men are terrified at what appears to be a ghost, Peter works up the courage to walk on water, at least for a few steps, before being rescued by Jesus. The disciples then bring Peter and Jesus on board (Matthew 14:27–33).
This verse describes the "bonus" miracle of John chapter 6: when the disciples take Jesus into the boat, they are "immediately" at their destination!