Referring to important era, old, in rebuilt chapel (7)
I believe the answer is:
epochal
'referring to important era' is the definition.
I can't judge whether this definition defines the answer.
'old in rebuilt chapel' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'in' is an insertion indicator.
'rebuilt' indicates anagramming the letters.
'chapel' with letters rearranged gives 'epchal'.
'o' placed inside 'epchal' is 'EPOCHAL'.
Can you help me to learn more?
(Other definitions for epochal that I've seen before include "Of a period in history" , "of a particular age" , "beginning a new era" , "typical of the age" , "of a certain age" .)