What does John 6:19 mean?

The Sea of Galilee is relatively small, only about 7 miles (11 km) long. Its position at the bottom of a series of high hills makes it prone to sudden storms and bursts of wind (John 6:18). At the time described here, the disciples are in the middle of a mess: a rough, stormy sea long before sunrise (Matthew 14:25; Mark 6:48). And yet, they are facing this challenge because of their obedience to Christ, who had commanded them into the boat in the first place (Mark 6:45). The object lesson there is relatively simple: hard times don't necessarily mean we're doing something wrong. On the contrary, obedience to God can involve inconvenience or even suffering (Acts 5:27–33).

The gospel of John skips over many of the details contained in Matthew, Mark, and Luke, assuming that the reader has access to those. However, a key point often missed in this story is given very clearly here by John, as well as Mark (Mark 6:49–50), as well as Matthew (Matthew 14:26). Namely, that the disciples don't fear the storm: they're afraid of Jesus! Their first assumption, on seeing a human figure walking over the waves, is that this is a ghost. While not the specific point of this story, it's worth keeping in mind that God's intervention in our lives can sometimes happen in ways we find unexpected, even frightening at first.

This is the fifth of John's seven signs: miracles used in this gospel to prove that Jesus Christ is God.