Either way he's Jesus' father (4)
I believe the answer is:
abba
'either way' is the definition.
'he's jesus' father' is the wordplay.
'he' becomes 'ab'.
'jesus' father' becomes 'ba' (I can't justify this - if you can you should give a lot more credence to this answer).
'ab'+'ba'='ABBA'
Can you help me to learn more?
(Other definitions for abba that I've seen before include "Biblical pop" , "rhyme scheme" , "camel-hair coat" , "striped coat?" , "Form of address to deity" .)