'Leaves' symbolize rational truths because a tree symbolizes a person, and every part of the tree symbolizes accordant elements in the person.

(Referências: Apocalypse Revealed 936; Arcana Coelestia 884, Genesis 8:11; Revelation 22:2)

884. 'And behold, in its mouth an olive leaf plucked off' means a small measure of the truth of faith; 'leaf' meaning truth, 'olive' good that stems from charity, 'plucked off' the fact that the truth of faith derives from that charity, and 'in its mouth' the fact that it was made visible. This is clear from the meaning of 'olive' and is evident from the very words themselves. That a tiny quantity is meant is clear from the fact that it was a leaf and no more.