Some people argue that the Church doesn’t officially teach that we believe that man can become like God (sometimes termed deification or theosis). Such a claim is simply untrue. I clearly remember teaching the doctrine as a missionary; it was on the very first page of the first discussion. Most Christians already believe that God is our Father, and that we are His children, and as such we can become like Him. Indeed, we should strive to become like Him.
It is likewise included in the new missionary guide Preach My Gospel, used by all current missionaries in the field:
God is the Father of our spirits. We are literally His children, and He loves us. We lived as spirit children of our Father in Heaven before we were born on this earth. We were not, however, like our Heavenly Father, nor could we ever become like Him and enjoy all the blessings that He enjoys without the experience of living in mortality with a physical body…
We are physically separated from God during life on earth, but He wants every one of His children to find peace in this life and a fulness of joy in His presence after this life. He wants us to become like Him. ((Preach My Gospel, 48))
This is the whole purpose of the gospel of Jesus Christ, to teach us and enable us to become like Christ, and hence like the Father. “Be ye therefore perfect, even as your Father which is in heaven is perfect” (Matthew 5:48).
The Church published a great article this month in the Church’s official magazine, the April 2013 Ensign, which reaffirms this foundational belief and teaching. The article is called “The Restoration and Early Christian Teachings,” by Michael R. Ash, who has done a lot of great work with FAIR. Here is a selection from that article, showing that theosis was an early Christian belief as well:
Heirs to the Father
Latter-day Saints believe that our Heavenly Father wants us to inherit all that He has so that we can become like Him and His Son. The Epistle to the Hebrews taught that Jesus is “appointed heir of all things” (Hebrews 1:2). Paul taught that the righteous will become “joint-heirs with Christ” (Romans 8:17), and Peter taught that they would be “partakers of the divine nature” (2 Peter 1:4).
Many early Christians believed that the righteous could become like the Father. Irenaeus wrote that Jesus Christ became “what we are, that He might bring us to be even what He is Himself.” ((Irenaeus, “Against Heresies,” in Ante-Nicene Fathers, 1:526.))
Clement of Alexandria wrote that Jesus became man so that we may “learn from man how man may become God” and explained that because the righteous will become so “near to the Lord, there awaits them restoration to everlasting contemplation; and they are called by the appellation of gods, being destined to sit on thrones with the other gods that have been first put in their places by the Saviour.” ((Clement of Alexandria, “Exhortation to the Heathen,” in Ante-Nicene Fathers, 2:174; and Stromata 7:10, in Ante-Nicene Fathers,2:539.))
Even as late as the third century, Hippolytus, bishop of Portus, explained that the righteous will become “a companion of the Deity, and a co-heir with Christ, no longer enslaved with lusts or passions, and never again wasted by disease. For thou hast become God.” ((Hippolytus, “The Refutation of All Heresies,” in Ante-Nicene Fathers, 5:153.))
The early Christian writings on deification are so extensive that non-LDS scholar G. L. Prestige stated that the early Christian Church “taught that the destiny of man was to become like God, and even to become deified.” ((G. L. Prestige, God in Patristic Thought, (1952), 73.))