When he is in Koshoji, Dogen writes almost all his Shobogenzo. And one of the talks he gives to priests and lay people can be read as a chapter: Bussho, Buddha nature. This is one of the 10 or 15 chapters that one should read, study, drink, eat, swallow, sweat, piss, do, undo, wieve, sew, bake, plow etc. More than a key chapter, it offers the most extraodinary journey through this all thing-non-thing that we are.
To start with, Dogen picks up this sentence:

The Buddha ??kyamuni said, “All living beings in their entirety have the buddha nature. The tath?gata always abides, without any change.”
And the rest of the talk is going to take it apart, take me and you apart,deconstruct view after view of the self, the Buddha and all the rest of it.
We don't have Buddha nature says Dogen, we are. And this is big. When the young Dogen was in Kyoto before his trip to China, he was puzzled by the simple question: if we already have it, why should we practice then? And of course, having a treasure, no need to look for it. As you operate a little shift of preception , it is not having Buddha nature but being Buddha nature, then, well, things get pretty clear, a Buddha practices a Buddha. Practice is not seen as a mean to get something you haven't got or you have forgotten you already had, it is about being who you are. And there is no other way to be a Buddha than being a Buddha.
Give it a go. And again and again. This chapter has treasures to reveal because you are the living revealed treasure!!!