The most common and most likely answer to this crossword clue is the 12 letter word RENUNCIATION
I've seen this crossword clue in The Times
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More clues leading to the result RENUNCIATION
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The straight part
We know that "a religious commitment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a religious commitment = renunciation.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.
Crossword Answer definitions
RENUNCIATION noun- The act of rejecting or renouncing something as invalid
- The resignation of an ecclesiastical office
- The act by which a person abandons a right acquired, but without transferring it to another.
- In the Anglican baptismal service, the part in which the candidate in person or by his sureties renounces the Devil and all his works.