The 2010 version of this lesson, which includes a discussion of the pseudepigrapha Book of Adam and Eve, can be found here: http://joelsmonastery.blogspot.com/2010/01/gospel-doctrine-lesson-4.html
The Tree of Life and the Endowment
The concept of the Garden of Eden and the Tree of Life are very ancient historically, and go back even to the ancient Babylonians.
Most modern scholars see a significant relationship between the tree of life in Genesis and similar trees or plants described in the literature of the ancient Near East. Though almost all cultures of the ancient world, especially the ancient Near East, possess soome kind of reference to the tree of life and humankind's quest to enjoy its fruit, there seems to be more profound connections between the Bible and the tree of life motifs in the oldest cultures of Mesopotamia than anywhere else. From an old Babylonian seal impression, now in the British Museum, the bilbical Garden of Eden scene appears to be clearly depicted, reflecting a "tradition that is no doubt of very ancient origin." In this scene, a tree stands in the middle, its boughs stretched out. On either side of the tree, two human figures are seated, each with an arm stretched forth, presumably to take the fruit of the tree. A serpent stands erect behind the figure on the left. The tree of life and the tree ofknowledge of good and evil are merged into one" (The Tree of Life: From Eden to Eternity, The Tree of Life in the Hebrew Bible and Later Jewish Thought, Andrew Skinner)
Because a tree can describe so many different concepts on many levels: tree, branch, leaf, fruit, roots, trunk, etc., it becomes the perfect symbol. The tree of life is believed in many stories to be in the center of Eden, and is viewed as the either the complement or the opposite of the Tree of Knowledge of Good and Evil.
The two trees represented two ways of knowing, perhaps two attitudes to knowledge, and the state that arises from each. The tree of life represented Wisdom, and those who ate from it were angels, "men." The other tree represented knowledge that could be used for good or for evil, and those who ate from it were mortals, "animals." The story of the two trees is the story of a clash of cultures: the life of the angels or the life of mortals. (The Tree of Life: From Eden to Eternity, The Tree of Life: The Fragrant Tree, Margaret Barker)In other words, there are two methods people try to become as God is. One is through Wisdom, and the other through the school of hard knocks (knowledge). Some traditions hold that God offered Wisdom to Adam and Eve, but Lucifer deceived them into the path of knowledge instead. They were changed from angelic beings into mortals, with the trials and tragedies that come with learning the hard way. They followed Lucifer's path of knowledge, one that opened the door to good and bad knowledge, but did not have wisdom. There was no saving power in the fruit of that tree, only death and suffering. A method of saving mankind from the necrotic side effects of the fruit from the tree of knowledge of good and evil would be needed.
In one of its symbolic forms, the Tree of Life is compared anciently to the woman Wisdom, consort/wife of God, sometimes called "Asherah". She represents not only Wisdom, but Life, fertility and rebirth. In John's Revelation, we learn that when the heavenly city appears, the tree of Life will be an integral part of the city, providing its immortal fruit to all the city's citizens. For Lehi and Nephi, the tree represented both the wife of God (in the symbol of Mary, mother of Jesus) and as the Messiah (in the form of the fruit of the tree of life).
The concept of the Tree of Life is also known in ancient America, where in the Popul Vuh, the dead God Hun Hunahpú is reborn when his head is planted inside a Calabash tree, and his seed (fruuit from from the tree)is dropped into a passing young woman, who bears twins that do marvelous works among mortals. From the story, we see a rebirth and a hope for the ancient Mayan world.
From Lehi's dream (2 Nephi 8-15) to the Popul Vuh to the story of the Garden of Eden, the Tree of Life represents redemption from a lost world. We are trying to return to the Garden, or as Nephi would put it, "the presence of the Lord". Adam and Eve lost access to the tree, and required a new path of return. The tree of life was now guarded by a flaming sword and cherubim (guardian angels). The Book of Mormon teaches us that the path to the tree of life entails rejecting the world's knowledge (represented by the great and spacious building) and embracing God's Wisdom. This does not mean we reject all of science, math, and literature. It means we need to realize that there is a greater thing to know out there: how to be like God in the manner that can make us god-like. Lucifer sought to overthrow God and his kingdom with the knowledge he had (Isaiah 14, Moses 4:1-4, Abraham 3). While knowledge can do many wonderful things (like create the computers and IPhones we now use), it pales in comparison to God's ability to create new worlds and to prepare them for his creation. He has the ability to forever restrain Chaos and Entropy, so that life can go on eternally. Knowledge cannot do all that is needed to hold off the dragon Leviathan from eventually consuming the earth and its inhabitants into the murky chaos of time and space.
Adam and Eve begin their exile by living a law of animal sacrifice and obedience. Only after years of learning through the life of knowledge and basic obedience that an angel is sent to ask Adam why he offers sacrifice. He has no reason, except for blind obedience. It is then that the angel gives to hiim the first bit of redeeming wisdom: this is done as a similtude of the Only Begotten, who is full of grace and truth (i.e., Wisdom). Adam and Eve are filled with the Holy Ghost and rejoice, for they are beginning the path back to the Tree of Life and the full presence of God. The stories about the Tree of Life are a form of endowment. It teaches us a higher goal than just working by the sweat of our brow, instead returning us back to the presence of God. It offers new and everlasting life through the fruit, Jesus Christ.
The Tree of Life: From Eden to Eternity, ed John Welch and Donald Parry
Nephi and His Asherah, by Daniel Peterson