Pastor Zac Poonen uses the two trees in the Garden of Eden - the tree of the knowledge of good & evil and the tree of life - to speak of the difference between living for self versus living for God.
We see these two trees symbolized in Scripture by two systems: Babylon and Jerusalem. What is the difference between the two? How do we know what it is to be religious versus what it is to be spiritual? It is not primarily the doctrine to which we hold. The answer is fire! The fire of the Holy Spirit.
Babylon is a Christianity of the head (knowledge, intellect). Jerusalem is a Christianity of the heart (devotion, passion).