| Quote #4
The speaker doesn't consider Porphyria's presence there to be a sin. For him, the real sin is her "weak[ness]" and "pride" – her unwillingness to throw off society's expectations and be with him forever.
| Quote #5
That moment she was mine, mine, fair,
The moment that Porphyria "worship[s]" the speaker, he decides that she's no longer committing the sin of "pride" and she becomes "perfectly pure and good."
| Quote #6
[…] I found
The murder of Porphyria, in the speaker's mind, isn't a sin at all – it's just "a thing to do." He's awfully casual about killing his lover.