Analysis of To Edward Fitzgerald

I chanced upon a new book yesterday;
I opened it, and, where my finger lay
'Twixt page and uncut page, these words I read -
Some six or seven at most - and learned thereby
That you, Fitzgerald, whom by ear and eye
She never knew, "thanked God my wife was dead."
Aye, dead! and were yourself alive, good Fitz,
How to return you thanks would task my wits.
Kicking you seems the common lot of curs -
While more appropriate greeting lends you grace,
Surely to spit there glorifies your face -
Spitting from lips once sanctified by hers.