Plato's Soul (Advice for living well)

This is me rambling about Plato's Tripartite Soul, how he reasoned to the three parts, the real meaning of the Republic, and why it all matters. I did not mention criticisms. The main criticism would be Kantian, where does the unity come from? That is, I'm aware of the three parts, so there must be some background unity, some "thing" uniting the three parts.