In jail Joseph meets Pharaoh's cup-bearer and thus gets an introduction to Pharaoh. You see how God's plan begins to work out slowly. It's not just that God protected Joseph from the evil that Potiphar and his wife did to him. He made the evil that they did to him to work out God's perfect plan. How would Joseph have ever met pharaoh's butler and got an introduction to Pharaoh if he hadn't gone to that jail!?!