The sea was stirred up because a strong wind was blowing. When they had rowed about three or four miles, they saw Jesus walking on the sea and coming near the boat, and they began to be afraid. But he said to them, “It is I. Do not be afraid.”
Job 9:8: God “treads upon the crests of the sea.” 🙂
To me, this miracle has a few aspects to be considered. It shows Jesus as having command over natural phenomena, like God. It shows the terror we can feel when confronted by the all-bets-are-off nature of suspended “reality”. And finally, Jesus says to not be afraid – he’s compassionate, and apparently, will intervene for our benefit.