Rehearse chapter at start of Thessalonians during worship (8)
I believe the answer is:
practise
'rehearse' is the definition.
(synonyms)
'chapter at start of thessalonians during worship' is the wordplay.
'chapter' becomes 'c'.
'at start of' says to take the initial letters (I've seen 'at start' mean this).
'during' means one lot of letters goes inside another.
'worship' becomes 'praise'.
The first letter of 'thessalonians' is 't'.
'c'+'t'='ct'
'ct' inserted into 'praise' is 'PRACTISE'.
(Other definitions for practise that I've seen before include "Train by repetition" , "Observe" , "Custom" , "Work" , "Contrive by some means" .)