The most common and most likely answer to this crossword clue is the 8 letter word PREACHED
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More clues leading to the result PREACHED
Buddy explains!

The straight part
We know that "gave sermon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gave sermon = preached.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 PREACHED mean?
PREACHED verb- To give a sermon.
- To proclaim by public discourse; to utter in a sermon or a formal religious harangue.
- To advise or recommend earnestly.
- To teach or instruct by preaching; to inform by preaching.
- To give advice in an offensive or obtrusive manner.