Exoteric knowledge is necessary. It is a prerequisite for those who would acquire esoteric knowledge. Just as there is a road to be travelled from metaphorical love to real love, there is also road that leads from exoteric knowledge to esoteric knowledge. The roads to God are as many as the different breaths we creatures breathe. Any aspect of exoteric knowledge can be the starting point for esoteric knowledge. If something has an exterior, it also possesses an interior. Only a fool would accept the one and not the other.
The exterior of the universe is visible to us, but that exterior hides an interior. Likewise, whatever has a beginning also has an end, and whatever has an end has a beginning. God is the First, the Last, the Outer, the Inner. He is the Creator of all things, and He knows their true nature. He is Allah, the All-Glorious.
Exoteric knowledge is the subject of sciences like logic, semantics, sociology, history, geography, mathematics and chemistry. One becomes learned in these sciences by a process of reading and study. To acquire esoteric knowledge, however, you must work with sincere devotion, practice constant remembrance of Allah, eat, talk and sleep but little, avoid unnecessary social contacts, and be completely receptive to a spiritual guide who is competent to direct you on the path of Truth. There is no other access to esoteric knowledge.
(The Garden of Dervishes; Sheikh Muzaffer Ozak al-Jerrahi, övers. Muhtar Holland)