Regularly called at new church that's firmly shut (6)
I believe the answer is:
clench
'firmly shut' is the definition.
I can't tell whether this defines the answer.
'regularly called at new church' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'at' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'church' becomes 'ch' (common abbreviation).
The alternate letters of 'called' are 'cle'.
'cle'+'n'+'ch'='CLENCH'
'that's' is the link.
Can you help me to learn more?
(Other definitions for clench that I've seen before include "Close fingers into a tight ball" , "Sharply contract (muscle)" , "Get a grip on" , "Squeeze together tightly" , "Close teeth or fingers tightly" .)