Brood about hard faith lessons in Jewish period (6)
I believe the answer is:
tishri
'jewish period' is the definition.
(I've seen this before)
'brood about hard faith lessons' is the wordplay.
'brood' becomes 'sit' (I've seen this before).
'about' says the letters should be written backwards.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'faith lessons' becomes 'ri' (I can't justify this - if you can you should give a lot more credence to this answer).
'sit' backwards is 'tis'.
'tis'+'h'+'ri'='TISHRI'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for tishri that I've seen before include "Jewish month; sir hit (anag.)" , "Jewish period" .)