The human heart is not generous enough to give up all, and be satisfied with the love of God. It wishes other things besides God, and because God will have no other love in His place, it fears the love of God which demands this sacrifice, and it sacrifices God instead.
I would love to look deeper into the poem one day. This poem managed to convert the hearts of a few English readers to the Catholic faith. A poem with that kind of evangelical power deserves a deeper look.
The poem is rather dense, though. There are words that I’ve never seen before (i.e. “dravest”). And analyzing a poem seems a luxury in time that I don’t remember having since my undergraduate years.
Fortunately, for the time being, I can use the insights from Fr. J.F.X. O’Conor, S.J.