The most common and most likely answer to this crossword clue is the 13 letter word EXCOMMUNICATE
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More clues leading to the result EXCOMMUNICATE
Buddy explains!

The straight part
We know that "cast out of Church" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case cast out of church = excommunicate.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 EXCOMMUNICATE mean?
EXCOMMUNICATE noun- A person so excluded.
- To officially exclude someone from membership of a church or religious community.
- To exclude from any other group; to banish.
- Excommunicated.