It was in middle of night and boat was being tossed in wind. The crew was stressed...
As if that wasn't enough, they were shocked to see someone actually walking on water through wind, rain, and waves. In Matthew 14 we're told of how crew was panicking. At first they thought that man was a spirit and they cried out in fear.
The man walking through storm told them to cheer up and have courage. He told them that "it is I" and not to be afraid.
Some of them had to have known His voice.
Peter answered man walking on water. He said, "If that is you, tell me to come out to you."
Jesus did. He said, "Come".
Peter got down out of boat to go to Jesus as he was told.
Really look at this. We are told in verse twenty-nine that "…And when Peter was come down out of ship…"
Preparing For Miracle
Evidently it took some time for that to happen. The testimony doesn't say how long it took or how Peter got down, but it does say that before he could walk on water to Jesus he had to do it
After time spent getting ready for miracle, Peter began to walk on water to Jesus!
But there was even some more time spent getting to goal. Peter took his eyes off of Jesus. Peter saw how windy it was. He was afraid.
The fear he felt was hook that made him start to sink.
Fear is opposite faith. No one pleases God without faith (Hebrews 11:6).
As Peter found out, fear is of enemy. He went from walking on water to a man starting to sink.
We're told that he began to cry and said, "Lord, save me" to Jesus.
Watching Physical Realm
How often do you and I see what's around us in physical realm, get afraid, and start to sink?
It's good news for us is in Matthew 14:31 that immediately upon Peter asking for help Jesus stretched forth his hand and caught him. He commented on doubt and little amount of faith that Peter had at time.