It helps one remember being churlish about Caesar’s opening comment (8)
I believe the answer is:
souvenir
'it helps one remember being churlish about caesar's opening comment' is the definition.
The definition suggests a singular noun which matches the answer.
'it helps one' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for souvenir that I've seen before include "remember seeing this?" , "Keepsake, memento" , "Reminder of holiday" , "Reminder of past events" , "something worth keeping" .)