Behold, how good and how pleasant it is for brethren to dwell together in unity! Psalm 133:1
Jesus Prayer for unity was more than just "Hey Father, I want these folks to hang out together and be together like we do".
He knew that outside of unity (did-unity) His power on this earth through His people, would be compromised. He wanted the world, I think, to have access to all He had to offer, through His people. Jesus knew that if we would truly come into unity, to love one another, that there would be nothing- nothing that could stand in the way of the world knowing Him.