Jenny has been doing some very sophisticated work on the Dews From Heaven blog, and I am trying to catch up to her thinking a little at a time! So once again I’m going to use my personal blogging space here to work out my thoughts before I post them there. :)
Okay, I think I’ve got it, but tell me if I don’t! :) I think what I see happening here is best visualized by a veil. Let’s say, for example, that the mysteries of the kingdom are on one side of the veil and we are on the other. God wants heaven and earth to come together, so we aren’t just going to leave the mysteries on one side and humans on the other. God brings some of the mysteries across the veil and if the humans will receive that, then they can come to receive more. By “some” here, I’m not thinking of this in a quantitative sense, but in a <i>qualitative</i> sense. I’m thinking of phrases like “first intimations” and “earnest of our inheritance.” It’s as if we receive a first layer of understanding. Then if we receive it in full faith, we can seek more. In this way, the mysteries constitute a key that allows us to seek more of the mysteries.
In D&C 128, I think Joseph is pointing out that we have a key to a mystery already. We can record priesthood ordinances. That seems like a simple thing, but he is telling us that we are not receiving that in the right way. When we come to see recording in relation to heavenly things, then it begins to serve as a key to a bigger understanding of what it means to record, bind, seal, etc.
So it isn’t that a key looks very different than the thing it unlocks. It isn’t a metal key to the Tardis, as Joe put it. :) It’s more like a condensed form or something like that. It’s given to us in a way that we can work with it by faith and prayer and then it opens up onto more mysteries. It expands, rather than unlocks?
So in the case of D&C 84:19, the idea might be that we can’t comprehend what the mysteries of the kingdom might be, so God adds the second part “even the key to the knowledge of God.” That very phrase is like a key that opens our understanding to what the mysteries in a general or bigger sense are. Is that at all what you’ve been getting at Jenny??