The number "two" has two different meanings in the Bible. In most cases "two" indicates a joining together or unification. This is easy to see if we consider the conflicts we tend to have between our "hearts" and our "heads" -- between what we want and what we know. Our "hearts" tell us that we want pie with ice cream for dinner; our "heads" tell us we should have grilled chicken and salad. If we can bring those two together and actually want what's good for us, we'll be pretty happy. We're built that way -- with our emotions balanced against our intellect -- because the Lord is built that way. His essence is love itself, or Divine Love, the source of all caring, emotion and energy. It is expressed as Divine Wisdom, which gives form to that love and puts it to work, and is the source of all knowledge and reasoning. In His case the two aspects are always in conjunction, always in harmony. It's easy also to see how that duality is reflected throughout creation: plants and animals, food and drink, silver and gold. Most importantly, it's reflected in the two genders, with women representing love and men representing wisdom. That's the underlying reason why conjunction in marriage is such a holy thing. So when "two" is used in the Bible to indicate some sort of pairing or unity, it means a joining together. In rare cases, however, "two" is used more purely as a number. In these cases it stands for a profane or unholy state that comes before a holy one. This is because "three" represents a state of holiness and completion (Jesus, for instance, rose from the tomb on the third day), and "two" represents the state just before it.

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.