A saint, but not without blemish (4)
I believe the answer is:
mark
'a saint' is the definition.
(I know that Mark is Saint)
'not without blemish' is the wordplay.
I cannot quite understand how this works, but
'blemish' could be 'mar' (I've seen this in another clue) and 'mar' is located in the answer.
A single letter 'k' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'but' is the link.
Can you help me to learn more?
(Other definitions for mark that I've seen before include "Brand - old German currency" , "that's no longer legal currency in Europe" , "Blemish" , "Note - evangelist" , "Starting point in race" .)