Either of two OT books briefly withdrawn before end of religious service (4)

I believe the answer is:

mass

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'religious service' is the definition.
(mass in a church)

I don't understand the remainder of the clue.

(Other definitions for mass that I've seen before include "Heap; religious service" , "seasonal midnight service?" , "Celebration of the Eucharist, especially in the RC Church" , "congregate for > service" , "Church rite; large group" .)

I've seen this clue in The Times.

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