When Jesus calls you to follow Him—and He never stops calling you to follow Him—He is calling you to take a step of faith. He doesn’t wait until you already believe before He calls you. He speaks to you where you are, in unbelief, just as He invited Peter to step out of the boat and walk to Him on the water.
When Jesus said, “Come,” Peter was still in the boat and still could not believe that he was looking a Jesus. The command of Jesus enabled Peter to step out of unbelief and into faith, just at it had done and would continue to do over and over again throughout his life.
This is an argument that Dietrich Bonhoeffer made in chapter two of The Cost of Discipleship. That first step of obedience is critical, he explained, and you can’t wait for faith to motivate you to take it because it itself is a step into faith.