Prof. Hugh Nibley said the following about the three stages of Adam:
“We are taught in the Kabbalah a great deal about the three Adams. There is the celestial Adam, who was Michael before he came here; the terrestrial Adam, who was in Eden; and the telestial Adam, after he had fallen, who was down low. The Kabbalah also tells about Jacob's ladder. Joseph Smith taught that it represented the three stages of initiation in the temple, the three degrees of glory…” 
Adam is the type that we humans follow in life. We come from a pre-earth life, from holier spheres. We come to this life and take upon ourselves a fallen and mortal nature. Then through the atonement of Christ, we repent and are sanctified to receive one of the three degrees of glory. The degree to which we are sanctified is up to us.
This is the purpose of the temple. We have the model in stone. The plan is taught. The ordinances of each degree are administered therein. The law that is required to receive each degree is taught and accepted by covenant.
And if we are faithful, we follow Adam to join the Family of God, as a joint heir with Christ.
There is no other way.
[1 - Hugh Nibley, Don E. Norton , Approaching Zion, Chapter 11, Deseret Book.]