Nuts, in short, about the Messiah, showing great zeal (10)
I believe the answer is:
enthusiasm
'great zeal' is the definition.
'enthusiasm' can be an answer for 'zeal' (I've seen this before). I'm not certain of the 'great' bit.
'nuts in short about the messiah' is the wordplay.
'in short' means to remove the last letter.
'about' indicates anagramming the letters.
'nuts' with its final letter taken off is 'nut'.
'nut' anagrammed with 'messiah' gives 'ENTHUSIASM'.
'showing' is the link.
Can you help me to learn more?
(Other definitions for enthusiasm that I've seen before include "Intense and lively interest" , "spirit?" , "Ardour" , "Avidity" , "Gusto; fervour" .)