It's useless and absurd to be only partly penitent (5)
I believe the answer is:
inept
'it's useless' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for inept that I've seen before include "Clumsy - silly" , "Silly or senseless" , "Awkward, showing no skill" , "rubbish" , "Foolish" .)