The most common and most likely answer to this crossword clue is the 13 letter word ANTHROPOSOPHY
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The straight part
We know that "spiritual ideology" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case spiritual ideology = anthroposophy.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 ANTHROPOSOPHY mean?
ANTHROPOSOPHY noun- (as used before Rudolf Steiner) Knowledge or understanding of human nature.
- A spiritual movement inaugurated by Rudolf Steiner (also capitalized as Anthroposophy), postulating the existence of an objective, intellectually comprehensible spiritual world accessible to direct experience through inner development.