In this conversation with Buddhadharma, the Insight Meditation Society cofounder applies the "harmonized understanding" approach championed in his book One Dharma to the idea of buddhanature. In the end, it's not about who's right or wrong about it. It's about what leads us to less clinging.
BUDDHADHARMA: Thanks for talking with us, Joseph. We're hoping you might talk about buddanature from your unique perspective as a Buddhist primarily trained in Theravada, but then in other modes, too. JOSEPH GOLDSTEIN: It's not a term that I've come across a lot in early Buddhist teachings; it seems to come about more in Mahayana and in Vajrayana. And so it would be helpful to find a common definition that would make sense in terms of early Buddhism. Basically, the Pali texts talk about the enlightened mind, free of defilements. That would, I think, be a good cross-tradition term.
In One Dharma, you list some of the names for the ultimate freedom that buddhanature represents: the unconditioned, dharmakaya, the unborn, pure heart, mind essence, nature of mind, ultimate bodhicitta, nirvana. Some of those terms are used more often in the later traditions. I think a popular understanding of some of the later traditions is that we're already enlightened, and we simply have to realize it. That might imply that it's more accessible than it actually is. Whether we phrase it in terms of "we're already enlightened and we just need to realize it," or "we're not yet enlightened and we have to get there," the task is formidable. (Read more here)