They involve a shift in one's beliefs (6)
I believe the answer is:
faiths
'one's beliefs' is the definition.
'faiths' can be an answer for 'beliefs' (faith is a kind of belief). I'm not sure about the 'one's' bit.
'they involve a shift in' is the wordplay.
'they' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'involve' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'shift' is an anagram of 'fiths'.
'a' going within 'fiths' is 'FAITHS'.
Can you help me to learn more?
(Another definition for faiths that I've seen is " Religious beliefs".)