How great a debtor, daily I'm constrained to be

Text: HT to Michelle H. for bringing to attention Satan's words in Paradise Lost Book 4:
I sdeind subjection, and thought one step higher [ 50 ]
Would set me highest, and in a moment quit
The debt immense of endless gratitude,
So burthensome, still paying, still to ow;
Forgetful what from him I still receivd,
And understood not that a grateful mind [ 55 ]
By owing owes not, but still pays, at once
Indebted and dischargd; what burden then?