The most common and most likely answer to this crossword clue is the 6 letter word GNOSIS
I've seen this crossword clue in Financial Times
G
N
O
S
I
S
More clues leading to the result GNOSIS
- Recalled what might be spiritual exists, knowing it?
- Sins go after getting renewed spiritual knowledge
- Carol uplifted by one’s spiritual awareness?
- Intuitive knowledge upset number one son
- Air about one’s spiritual knowledge
- Number turned against terrorist group’s spiritual knowledge
- Blur song is result of conceptual process
- Numbers taken in by soldiers offering knowledge
- Spiritual knowledge is breaking into song making a comeback
- Good little girl accumulates no special knowledge allegedly
Buddy explains!

The straight part
We know that "spiritual knowledge" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spiritual knowledge = gnosis.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does GNOSIS mean?
GNOSIS noun- (gnosticism) an immanent form of knowledge or transcendent insight, such as sought by the Gnostics
- Act or process of knowing
- An altered state of awareness in which the will is magically effective