First: Nymphs and prayers are not usually coupled. Nymphs being quite Greek, quite pagan, quite nature cult and orisons being a sort of ritualized prayer, specifically Christian, I think? It’s a very interesting pairing.
Second: Why does he want her to remember his sins in her prayers? Does he somehow need her to absolve him? Or is he thinking of sins the two of them might have enjoyed in the past and he’s claiming them for himself? Is he asking her to pray for him? What would these prayers sound like in his imagination?
“Dear Lord, please forgive Hamlet for scaring the beejeezus out of me in my sewing closet the other day and for acting crazy and for seducing me behind the chapel that time and in the gazebo and the library and so on. Oh and that one time, he took your name in vain. Well, I’m sure it was more than that one time, lord, but I only heard it that once. Let’s see – he’s maybe not honored his mother so much lately. As far as I know, he’s never committed adultery or murder or theft so I think he’s good there. Well, anything I’ve forgotten, lord, just go ahead and forgive him for that, too – because I’m sure he’d like you to.”
The Hamlet Project 