There are two aspects to the life of each person. We might call them "heart" and "mind," a part of us that wants and feels and a part of us that thinks and knows. The Writings usually refer to these as the "will" and the "understanding." They are reflections, and receptacles, of the Lord's infinite love and infinite wisdom. Of the two, the heart or will is ultimately the most important. Who we actually are is determined by what we love, and the things in our heart ultimately determine our place in heaven (or hell). But the will is beyond our control; we can't force ourselves to want something good or to not want something bad; we can control our actions, but not our feelings. Because of this power, the Lord works subtly and carefully in our hearts, in ways we can't sense. Most of the work and interaction goes on in our minds through the working of what the Writings call "Divine Truth," which is essentially the Lord's entire essence expressed in a form that is compatible with our minds. When the Bible talks about the Lord's "spirit," it represents this operation of Divine Truth in our minds, the way he reaches out and embraces us, and invites us to embrace him back. And when the Bible talks about people having "spirit," it is talking about our minds when we embrace Divine Truth.

In general, trees represent the deepest and most significant intellectual concepts: the ones that come to us most directly from the Lord. This varies depending on us and our states: the people of the Most Ancient Church, who were in a state of loving the Lord, understood truth automatically and internally through what the Writings call "perception"; people in lower states (including most of us) have to work a little harder to learn it from the Word and by willing to follow the Lord. In other parts of the Bible, especially in the prophets and New Testament parables, the meaning of "tree" is broader, meaning not just a person's intellectual concepts but the whole person.

'Trees,' as in Joel 1:10-12, signify knowledges.