Satisfied Gospel's top grade (4,5)

I believe the answer is:

full marks

I'm a little stuck... Click here to teach me more about this clue!

'top grade' is the definition.
I don't know anything about this answer so I can't judge whether it can be defined by this definition.

'satisfied gospel's' is the wordplay.
'satisfied' becomes 'full' (e.g. after eating).
'gospel's' becomes 'Mark's' (book of the New Testament).
'full'+'marks'='FULL MARKS'

Can you help me to learn more?

(Other definitions for full marks that I've seen before include "Well done!" , "One-hundred percent" , "Maximum score" .)

I've seen this clue in the Sydney Morning Herald.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.