In not always so (on p. 17 of my copy):
Sometimes we say Buddha nature. Sometimes we say enlightenment or bodhi, Buddha or attainment. We call Buddha nature not only by these names, but sometimes we call it "evil desires." We may say evil desires, but for Buddha, that is Buddha nature.
In the same way some people may think that laypeople and priests are fundamentally different, but actually there is no particular person who is a priest. Each one of you could be a priest, and I could be a layperson. Because I wear a robe I am a priest, and I behave like a priest. That's all. There is no innate nature that distinguishes priest from layperson.
Whatever you call it, that is another name of one reality. Even though you call it a mountain or a river, that is just another name of the one reality. When we realize this, we are not fooled by words like "nature," "result," or "Buddhahood." We see things themselves with a clear mind. We understand Buddha nature in this way.
"Evil desires" is another name for Buddha nature. When we practice zazen, where would evil desires come from? In zazen there is no place for evil desires. Still we may believe that evil desires should be eliminated. Why is that? You want to eliminate your evil desires in order to reveal your Buddha nature, but where will you throw them away? When we think that evil desires are something we can throw away, that is heretical. Evil desires is just a name we use, but there is no such thing we can separate out and throw away.