Know thy Bible. And know thyself. But just a heads up: you have to know thy Bible, first, in order to begin to know thyself. 

The Bible is a great book. Grand, indeed. We learn about God (theology). We learn about ourselves (anthropology). We learn about the rest of creation (cosmology).

But we don’t only learn about all these things, we also learn what God thinks about them, which in some corners of this world, where they (typically) use archaic, big words and obscure phrases, is referred to as the “doctrine of the knowledge of God.” And if you want to know thyself, then you have to begin with what God says you is.