The very fact that islamic peoples kept this ‘religion’ until today, unable to understand how fake it is, proves that chances for a real spiritual growth practically equal zero.
What other example could be more characteristic than what happened with Constantinople?
Six centuries after its fall, Constantinople is still known to the world and admired as a Byzantine city!, the City, while Islam proved unable to make with her anything whatever matching (to any degree) the history of Byzantium.
If the Ecumenical Patriarchate was not there until today, Constantinople would have been nothing more than an overcrowded turkish habitation. They thought they grasped the greatest treasure of all, ignoring that real treasures are not of space and time, where they only leave some traces, quickly disappearing from the eyes of unholy people.