Here we may observe fully developed the doctrine of passing away in God ( ) which from time onwards assumes a central position in the structure of Sufi theory. It was after all not a difficult transition to make from saying that all else but God is nothing (which is the logical outcome of the extreme ascetic teaching that the world is worthless and only God's service is a proper preoccupation of the believer's heart), to claiming that when self as well as the world has been cast aside the mystic has passed away into God.