Help interpreting this poem?

This poem is talking about Sarah Anna Lewis, a poetess that helped Poe through some hard times. This is a sonnet with iambic pentameter. He is saying that this poem has more substance within it than others, but given his last few lines, I would venture to guess that he is saying that the true meaning lies not within the lines, but in the name that he hid. It is immortal, because she is immortal, and knowing little fame in his own life, he has given longevity to his sonnet by attaching it to another artist.