"... but the boat by this time was a long way from the land, beaten by the waves, for the wind was against them. And in the fourth watch of the night he came to them, walking on the sea. But when the disciples saw him walking on the sea, they were terrified, and said, “It is a ghost!” and they cried out in fear. But immediately Jesus spoke to them, saying, “Take heart; it is I. Do not be afraid.”

And Peter answered him, “Lord, if it is you, command me to come to you on the water.” He said, “Come.” So Peter got out of the boat and walked on the water and came to Jesus. But when he saw the wind, he was afraid, and beginning to sink he cried out, “Lord, save me.” Matthew 14.24-30 ESV

The disciples thought they saw a ghost and then they heard that "ghost" said he was Jesus. Peter tested that "ghost": if you are who you said you are (i.e. Jesus), then you can make me walk on the water.

Peter had faith that Jesus could make him walk on the water. But he was not sure if that was Jesus or not.

Sometimes in our lives, we face a situation where we thought we had to act on faith. But before we exercise that faith, let us be sure that it is indeed God, not our ego or earthly desire that put us in that situation.

If God does not call us to walk on the water, we will not be able to, no matter how much faith we think we have.

We exercise our faith when we act on God's call. And when God calls, look unto him as the source of our faith so we will not sink.