Notice I intended to limit chapter's importance (12)
I believe the answer is:
Here is my best explanation:
'importance' is the definition.
(significance is a kind of importance)
'notice i intended to limit chapter's' is the wordplay.
'notice i' becomes 'signi' (I can't explain this - if you can you should give a lot more credence to this answer).
'intended' becomes 'fiance' (I've seen this before).
'to limit' means one lot of letters goes inside another.
'chapter' becomes 'c'.
'fiance' placed around 'c' is 'ficance'.
(Other definitions for significance that I've seen before include "Importance, meaning", "Import", "Meaning" and "weight".)