The tension between God's sovereignty and our choice is illustrated by Peter's steps on the water. Peter realizes Jesus provides the power, but he must contribute his faith. He must walk out to Jesus courageously.
Jesus' verdict on Peter's action is that he has a degree of faith but needs to work on doubt. For us to walk on the water and overcome evil, we must make a free-will decision to put our faith in the master. Like a stepping stone in the sea, he will then guide our path.