It's rude to raise your voice.
The parishioner is attending a sermon in a crowded church.
The parishioner wants to be a good member of the church.
The parishioner preserves his quiet demeanour and attempts silently to assist the man in the pew.
The parishioner yells during the service when they see a man sliding off the pew.
The parishioner is gratified that he could preserve the composure of the church service.
The parishioner feels guilty for disturbing the service, but also glad he could assist the man.