Initially I thought it was about rationally understanding the three principles. But, the true genius of this book, that I've come to recognise, is how all three principles blend together and relate to one another in practice. And when one does it the result is just wonderful.
I forgot Plato was banned. I was going to ask him(?) if Truth-Love-Power reminded him of Plato's three philosophical concepts: Virtue (truth), Eros (appetites/desire/love), and Thumos (courage/discipline). Thumos is what brings Virtue and Eros together into action. Unfortunately, I did not find Plato very helpful for putting those ideas into practice, though they were interesting to read about. I think Aristotle talked even more about discipline / the Middle Way / thumos, that thing in between extremities, but I didn't find him particularly helpful either compared to reading about Zen.
I just read the Introduction in PDSP, and the first thing I thought of when I read the three core principles was Plato. I'm sure this book does a better job at explaining thumos than Plato did.