The most common and most likely answer to this crossword clue is the 6 letter word HOMILY
I've seen this crossword clue in The Sunday Telegraph
H
O
M
I
L
Y
More clues leading to the result HOMILY
Buddy explains!

The straight part
We know that "sermon" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sermon = homily.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 HOMILY mean?
HOMILY noun- A sermon, especially concerning a practical matter.
- A moralizing lecture.
- A platitude.