In this sonnet, a man is sits through a catholic mass, praying, singing hymns, listening to the sermon, and took communion. He is nervous and uneasy. "...after the hand-wringing..." (687) He lets his mind wander for a time while noticing the shafts of light through the window, revealing particles of dust dancing over in the sanctuary, this still does not take the pain away. So he confesses, but he still feels the pain of what he has done. He still can't cleanse the spilt blood from his conscience.
An English rhyming scheme is ababcdcdcdefefgg, the Italian Scheme's first eight lines are abbaa and the last six lines are cdecde, cdcdcd, or cdccdc. This particular sonnet utilizes part of the Italian rhyming scheme because it is abbaa cdecde.
The use of the words "after" and "there" is a demarcation of time. It divides the sonnet into two parts, one of action, and one of thought.
The first part is everything he does to try to feel better, and the second part states that it was all in vain because he can't atone for his sin of murder.
A Communal is a confession of sins. He took a stab at trying to relieve his guilty conscience by confessing his sin of murder, but he didn't understand that confessing would not atone for what he had done. His conscience still plagued him. Since this was the result, the statement "communal stab," was totaly accurate. He took a stab - chance that if he confessed, he would find relief from his tormented soul.