Peace of mind provided by letters read aloud (4)
I believe the answer is:
ease
'peace of mind' is the definition.
(thesaurus)
'letters read aloud' is the wordplay.
'letters' becomes 'es' (more than one E).
'read aloud' shows a homophone (sound like).
'es' sounds like 'EASE'.
'provided by' acts as a link.
(Other definitions for ease that I've seen before include "Absence of difficulty" , "Free from pain" , "Leisure, relaxation" , "State of relaxation or rest" , "Effortlessness" .)