Arcana Coelestia # 95
95. The subject here is the life of the external man. In the two previous verses it was the life of his faith or understanding, now in this verse the life of his love or will. Previously the external man was not willing to comply with or serve the internal but constantly struggled against it, and so the external man at that time was not man. But now that he has become celestial the external man starts to comply with and serve the internal, and becomes man as well - in particular through the life inherent in faith and the life inherent in love. The life of faith prepares him to be man, while the life of love actually makes him so.
Tree
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.