Religious instruction that could be schematic (9)
I believe the answer is:
catechism
'religious instruction' is the definition.
(question and answer method of religious teaching)
'could be schematic' is the wordplay.
'could be' indicates an anagram.
'schematic' anagrammed gives 'CATECHISM'.
'that' acts as a link.
(Other definitions for catechism that I've seen before include "Schematic for religious questions-and-answers book" , "Schematic for religious principles in question and answer format" , "Set of questions for religious teaching" , "summary of belief" , "Schematic for summary of religious principles" .)