Thank you for the music: Through a Glass, Darkly

To answer the riddle that Master Garrett puts to me, I must have two things:
I immediately find myself thinking along the lines of "eye of toad, and wing of bat..."
Doctor Dee continues to explain:
A lock, and a key. Our Lock is an item of knowledge, but not how it may be used. Our Key is he that hath understanding to use what is known, but possesses not the Lock.
And am I one of these two, Doctor Dee?
You are. Or more properly, what you have told us of last night is the Key. Now it is for Doctor Kelley and myself to find the Lock and apply the Key. And in order that the Key may open the lock, we shall also have need of you if you are willing?
How do you propose to use me?
If you will, get you to the priest and be shriven and fast until the seventh hour today when you shall come here and join myself and Doctor Kelley in a scrying for the Lock.
I followed the instructions given, firstly seeking confession with the village priest. I never imagined I might have accumulated so many sins until he suggested a list of possible headings! And although Master Garrett wasn't keen on the idea, I was given leave to make my way to the house of Doctor Dee. By the time the seventh hour rolled around I think I could have recited the pater noster backwards and my tummy was rumbling quite noticeably.

Doctor Kelley's study was surprisingly tidy; a couple of shelves held ancient-looking books, and such furnishings as there were had been moved back against the walls to make room for a small table in the centre of the room on which lay a bundle wrapped in black velvet. Doctor Dee bade me be seated, and carefully unwrapped the velvet bundle to reveal a slab of polished obsidian.
Now Doctor Dee picked one of the vials from the collection on Doctor Kelley's desk, uncorked it, and using the feather end of an uncut quill, proceeded to draw a faint circle encompassing the chairs and table where I was seated. At each of the cardinal points of the compass, he added an obscure symbol and invoked the protection of one of his familiars; I remember the names of Il, Po and Va but forget the fourth.
Finally Dee and Kelley settled themselves around the table equidistantly we joined hands and Doctor Kelley advised me to close my eyes and recall as clearly as I might, every detail of the night before when I was awoken.
With eyes closed, I listened to Doctor Kelley murmuring what seemed at first to be random phrases; a cat cries, a rat finds an apple core, the mice scratch at their fleas. I know my mind started to wander, and I may have missed something, but when he said The heaven opens and the seeker descends! I came back to earth with a start. I am afraid my surprise disturbed the mood and if neither of the Doctors had said anything I still would have known that they were less than pleased with my conduct. However, they did at least confide that they felt something had been achieved, even if they did not elect to enlighten me further.
Leaving the house of Doctor Dee in the dark, my spirits were thoroughly cast down and I would happily have slunk back to Master Garrett's loft to break my fast with a cold pie but on my way back into the village Peter and his sweetheart, Susan siezed me one by each arm and frogmarched me to the tavern, refusing to let me leave once more until I had lined my belly, drunk good cider, and danced a measure or two.