The teaching of early Jewish priests found in a booklet or a handbook (5)
I believe the answer is:
torah
'the teaching of early jewish priests' is the definition.
I can't judge whether this definition defines the answer.
'in a booklet or a handbook' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TORAH' is hidden in the letters of 'booklet or a handbook'.
'found' is the link.
Can you help me to learn more?
(Other definitions for torah that I've seen before include "The whole body of Jewish religious literature" , "The body of Jewish sacred writings and tradition" , "Jewish law" , "Jewish scripture" , "The law of God as revealed to Moses" .)