Tree of Life
"In the book of Genesis Adam and Eve were banished from Eden and forbidden to eat from the tree of life, which would give them immortality. As used in the text (of the Prism of Lyra), the tree of life represents knowledge of the divine relationship between human beings and the Creator, thus revealing that our spirituality is not dependent upon those who genetically engineered us." (PoL)
The tree of life is one of the two trees mentioned in Genesis 2-3. The other one was the Tree of Knowledge of Good and Evil. Eating the fruit of the tree of life was supposed to give eternal life.
The Tree of Life also is the main symbol of the Cabala, consisting of ten sefirot and twenty-two paths connecting the ten sefirot. Penny Cohen describes the Tree of Life as "a ladder or map of existence. It shows the functions, structure and dynamics of the universe. It also shows the evolution of human consciousness." (Penny Cohen, Personal Kabbalah, p. 8).
There are two main variations of the Tree of Life: the Lurianic and the Cordovero. In the Lurianic version there are paths between Chokmah and Gevurah, and between Binah and Chesed, whereas the Cordovero does not have these, but has paths between Netzach and Malkhut and between Hod and Malkhut instead.
Just as there are 22 pathways in the Tree of Life, there are 22 letters in the Hebrew alphabet, and each pathway is assigned a letter. Unfortunately virtually every other author has his own version of these correspondences.