Concerning the subject at hand--how the Mormon Church differs substantially from biblical Christianity--there is an overwhelming amount of available information. Far, far too much for us to even begin to scrape the surface here (I have included some relevant links at the end of this post for those interested). In light of that, I have not attempted an exhaustive or definitive, but have instead endeavored to lay out just a few facts that uphold the claim that biblical Christianity and Mormonism are quite distinct. Please note that in showing the doctrines of the Mormon Church, I have used only their own sources.
Finally, as I stated two days ago, these beliefs do not make it impossible for Mitt Romney to serve well in political office. The object of this article is to let the truth be known in the event that his upcoming speech would lead listeners to believe that Mormonism and Christianity are on the same page. So, let's begin...
The Mormon Church, in contrast to Christian churches, accepts four books as authoritative Scripture: The Bible; The Book of Mormon; The Doctrine and Covenants; and The Pearl of Great Price. This gives them three more holy books than Christians. For biblical Christians, the Bible is the only authoritative rule of faith and practice, the only book inspired by God. This is a huge difference in and of itself.
Of course, if you have three extra books, you're bound to have some extra ideas. That is certainly the case, here. I've decided to take time only to delve into two of these extras (that alone will take plenty of space, as you may have already noticed). First, how the Mormon Church's view of God differs greatly from Christianity's, and second, how their view of the identity and longevity of the church differs.
I. The Nature of God
A. There is one God
A. There is one God
A1. The Bible teaches us that there is but one God. In Isaiah 43:10, we read, "Ye are my witnesses, saith the LORD, and my servants whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me." Later in the same book, God says, "...I am the first, and I am the last; and beside me there is no God" (Isaiah 44:6). Finally, as if to make sure the point is driven home, the book of Isaiah offers us a third passage on the subject: "Fear ye not, neither be afraid: have not I told thee from that time, and have declared it? ye are even my witnesses. Is there a God beside me? yea, there is no God; I know not any." Other passages speak to this same truth (Deut. 32:29; 2 Sam. 7:22; 1 Chron. 17:20; Mk. 12:32; 1 Co. 8:6; 1 Tim. 2:5; Js. 2:19).
A2. The Mormon Church believes there are three Gods. In the fourth chapter of their Book of Abraham, which is a part of the Pearl of Great Price, you can read many time over of how "the Gods" created the universe (Abraham 4-5). Joseph Smith, the Mormon prophet, said himself: "I have always declared God to be a distinct personage, Jesus Christ a separate and distinct personage from the God the Father, and that the Holy Ghost was a distinct personage and a Spirit: and these three constitute three distinct personages and three Gods" (Teachings of the Prophet Joseph Smith, p. 370). They also believe in a multiplicity of other gods (gods, with a lower case "g"), as expressed in Doctrine and Covenants 121:32 and 132:20.
B. God has always been God
B1. The Bible teaches that God has always been God. Psalm 90:2 reads, "Before the mountains were brought forth, or ever thou hadst formed the earth and world, even from everlasting to everlasting, thou art God." God has always been, and always will be, God (see also Psalm 93:2).
B2. The Mormon Churches teaches that God was once a man! Their prophet, Joseph Smith, said the following: "God himself was once as we are now, and is an exalted man, and sits enthroned in yonder heavens!...I am going to tell you how God came to be God. We have imagined and supposed that God was God from all eternity. I will refute that idea, and take away the veil, so that you may see...[H]e was once a man like us; yea, that God himself, the Father of us all, dwelt on earth, the same as Jesus Christ himself did..." (Teachings, pp. 345-347, quoted from Mormon Doctrine, Bruce R. McConkie, p. 321, under "GODHOOD").
C. God is a spirit
C3. The Bible teaches that God is a spirit, and does not have a body of flesh and bone. In John 4:24, we read: "God is a spirit...", and Jesus affirms that "...a spirit has not flesh and bones..." (Luke 24:39).
C4. Mormon doctrine affirms that God, who "is an exalted man" is not a spirit, and that he has a body of flesh and bone. In Doctrine and Covenants 130:22, we read: "The Father has a body of flesh and bones as tangible as man's; the Son also; but the Holy Ghost has not a body of flesh and bones, but is a personage of the Spirit...."
II. The Existence and Identity of the Church
A. Christianity teaches that "the church" (Christ's body of saved believers on earth) has been in existence since its inception in the first century. It acknowledges that there have been many down through the centuries who erroneously identified themselves as "the church", yet affirms that the church, "the kingdom of God" on earth, persisted all the while. In Daniel 2:44, Daniel speaks of the future establishment of the church, and says, "...the God of heaven will set up a kingdom which shall never be destroyed...and it shall stand for ever." And centuries later, just prior to Jesus' birth, the angel Gabriel said to Mary that "...of [Jesus'] kingdom (the church, Colossian 1:13) there shall be no end" (Luke 1:33).
B. The Mormon Church teaches quite the opposite. They teach that the true church actually disappeared from existence soon after the death of the apostles, and that it didn't resume existence until over a millennium later, due to the work of their prophet, Joseph Smith. According to Joseph Smith himself, he was told by God when he was a youth that none of the churches in existence in his day were right: "I was answered that I must join none of them, for they were all wrong" (History 1:19). In keeping with this idea, he was later directed by God to bring "the truth" to those around him, and restore the church. Of course, this goes hand-in-hand with LDS church's claim that it is "the only true and living church upon the face of the whole earth" and that "the power of God unto salvation--(Rom. 1:16) is absent from all but the Church of Jesus Christ of Latter-Day Saints" (Bruce McConkie (a Mormon apostle), Mormon Doctrine).
Time and space fail here, but there is so much more that could be said. We could discuss how the Mormon Church's idea of the afterlife, the priesthood, salvation, and spiritual discernment differ extremely from biblical Christianity. Though they use the same words as Christians, they mean entirely different things when they say them.
We live in a free country, and that's something to be thankful for. The Mormon Church is free to teach and believe what it does. Its members are even free to say what they want about how their faith relates to Christian faith. But regardless of what is said, the truth will not change. "Facts are stubborn things," said John Adams.
Newsweek seems to have summed it up well: "[Mormonism] now insists it be regarded as a Christian church, albeit one with doctrines about God, salvation and priesthood that differ radically from traditional Christianity" (Newsweek, September 10, 2001).