The cost of being a disciple of Jesus is that we don't follow our own will, but the will of Jesus our master.
This idea is found in the New Testament of the Bible, specifically in Luke 9:23-24 where Jesus tells his disciples that if anyone wants to be his follower, they must deny themselves and take up their cross daily, and follow him. This means that as disciples, we must put aside our own desires and follow the will of Jesus, even if it goes against our own interests or comfort.
While it's true that following Jesus can involve fighting against the devil and facing persecution from the world, the central aspect of being a disciple is surrendering our will to Jesus and following him wholeheartedly.