According to Daniel Burke writing for the Religion News Service and published in the SLTrib (5 Jan 2012):
[Joseph] Smith preached fairly orthodox Christian theology at first, but “became increasingly radical, breaking more and more from standard Christianity with every year that he lived,” said Craig Blomberg, a professor at Denver Seminary who has been active in evangelical-Mormon dialogue.
A sermon Smith preached [the King Follett discourse] three months before his death in 1844 planted the seeds for Mormonism’s biggest break with traditional Christianity, according to scholars. In it, Smith preached that God was once a flesh-and-blood man who had attained godhood. Likewise, Smith taught, humans could advance to God-like status in heaven.
“It has become important for traditional Christians to maintain an unbridgeable creature-Creator chasm,” said Robert Millet, emeritus dean of religious education at Mormon-owed Brigham Young University in Provo.
“For Latter-day Saints, God and man are the same species. God has substance — he is not just a force or power. He is an exalted, glorified man, and one of the purposes of the gospel is to help us become what he is.”
The idea of humans becoming gods runs counter to mainstream Christianity, said Richard Mouw, president of the evangelical Fuller Theological Seminary in Pasadena, Calif. Confusing the two has traditionally been considered blasphemous, he said.
However, the Mormon idea does approach the Eastern Orthodox Christian notion of “theosis,” or partaking in the divine energies of God, said Mouw, a 20-year veteran of Mormon-evangelical dialogue.