Add page to one set of religious books, and go after expression of uncertainty (10)
I believe the answer is:
interleave
'add page to one set of religious books' is the definition.
I can't judge whether this defines the answer.
'go after expression of uncertainty' is the wordplay.
'go' becomes 'leave' (go can mean to depart or leave).
'after' means one lot of letters go next to another.
'expression of uncertainty' becomes 'inter' (I can't justify this - if you can you should give a lot more credence to this answer).
'leave' after 'inter' is 'INTERLEAVE'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for interleave that I've seen before include "Insert between (book) pages" , "put in blank pages" .)