Part 2 here.
Part 3 here.
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Mormons believe that our Heavenly Father and our Heavenly Mother begat us as “spirit children.” Well, among these “spirit children” were two brothers—named Jesus and Lucifer. Again, I am NOT making this up. Jess L. Christensen, an area authority in the LDS church, wrote an article in the June, 1986 issue of the magazine called Ensign, which is an OFFICIAL publication of the LDS church, and is considered to be authoritative by Mormons:
On first hearing, the doctrine that Lucifer and our Lord, Jesus Christ, are brothers may seem surprising to some---especially to those unacquainted with latter-day revelations. But both the scriptures and the prophets affirm that Jesus Christ and Lucifer are indeed offspring of our Heavenly Father and, therefore, spirit brothers…as the Firstborn of the Father, Jesus was Lucifer's older brother. (1)
Many Mormons seek to deny that this doctrine is taught, or ever was taught. There you have it, in black and white, right before your eyes. Does that sound like the true Christ? See, Lucifer was an angel, a created being. And if Christ was his brother that means that Jesus must have also been created. But we know that our Lord Jesus Christ is the uncreated, everlasting, eternal Son of the uncreated, everlasting, eternal Father. “From everlasting to everlasting, THOU ART GOD!!” Listen to what it says in Nehemiah 9:6

So, what about creation? How did that happen? Well, apparently, GOD the Father called a meeting with His spirit children, to figure out a way that they could continue toward godhood. Joseph Smith:
In the beginning, the head of the Gods called a council of the Gods; and they came together and concocted a plan to create the world and people it. (2)
One fellow who has studied this subject put it this way:
God presented to his children…a plan of salvation for their consideration. This plan was to be the means by which God's spirit children could continue their growth and development and thus attain exaltation. A world would be created—this earth—where they would be born of mortal, human parents and receive a body of flesh and bones. And they would not remember their premortal lives with their Heavenly Parents.
[…]
Two of God's children volunteered to serve as the world's redeemer: Jesus Christ, the first-born and eldest of all, and Lucifer, another spirit-child.
[…]
Ultimately, God chose Jesus Christ to serve as the savior and redeemer of the world. One third of all God's spirit children, however, took the side of Lucifer and rebelled against God. A war in heaven ensued; Lucifer and the rebellious spirits were finally cast out…
Genesis 1:1



So, what do they teach about the fall of Man—Adam’s sin that brought death into the world? The LDS church considers the fall of man to be a GOOD thing. Another of their “scriptures” is called “The Pearl of Great Price,” and it contains something called “The Book of Moses”. Moses 5:10-13,
[Adam said]…because of my transgression my eyes are opened, and in this life I shall have joy…And Eve, his wife, heard all these things and was glad, saying: Were it not for our transgression we never should have had seed, and never should have known good and evil...
Another passage from the Encyclopedia of Mormonism says this:
These sources [the Mormon “scriptures”] dwell at length on the beneficial effects of the Fall as part of God's "great plan of happiness" for his children and testify that Adam and Eve are to be honored for their actions. (4)
But what does the Bible say about this event? Genesis 3:6-8

Next, we’re going to see what they believe about the virgin birth of Christ. Consider the following passages from the Bible.
- Matthew 1:18
—Now the birth of Jesus Christ was as follows: After His mother Mary was betrothed to Joseph, before they came together, she was found with child of the Holy Spirit.
- Luke 1:34-35
—Then Mary said to the angel, "How can this be, since I do not know a man?" And the angel answered and said to her, "The Holy Spirit will come upon you, and the power of the Highest will overshadow you; therefore, also, that Holy One who is to be born will be called the Son of God."
"The Church of Jesus Christ of Latter-day Saints proclaims that Jesus Christ is the Son of God in the most literal sense. The body in which He performed His mission in the flesh was sired by that same Holy Being we worship as God, our Eternal Father. Jesus was not the son of Joseph, nor was He begotten by the Holy Ghost." (5)
The First Presidency and Council of Twelve said in 1916,
"Jesus Christ is the Son of Elohim both as spiritual and bodily offspring; that is to say, Elohim is literally the Father of the spirit of Jesus Christ and also of the body in which Jesus Christ performed His mission in the flesh..." (6)
So you see, they don’t believe that Jesus was conceived by the Holy Spirit, but by the Father. In fact, they don’t even believe in the Virgin Birth of Christ the same way we do. What they say is that Mary was a virgin when our Heavenly Father—literally—had sexual intercourse with her and conceived Jesus Christ in the flesh. This, my friends, is NOT THE TRUE CHRIST.
So, GOD learned how to be GOD, he bore “spirit children” with Heavenly Mother, two of which were the brothers Jesus and Lucifer. He created the universe, and put Adam and Eve in the garden of Eden where they sinned against GOD—which was a good thing. Because it gave us all the chance to become “gods” ourselves. I’m not making this up. But Joseph Smith did. If we live a good enough life, get married, have a bunch of kids, etc., we too can become a “god”…just like GOD. Again, Joseph Smith, from the King Follett Discourse:
Here, then, is eternal life—to know the only wise and true God. And you have got to learn how to be Gods yourselves…until you are able to sit in glory as do those who sit enthroned in everlasting power. (7)
And the thing is, this “progression” doesn’t stop when we die. See, there are three “heavens” in Mormonism. The telestial for murderers, adulterers, and those who were Mormons but left the LDS church. The terrestrial is for “good people” who weren’t Mormons. The highest heaven—the celestial—is for Mormons who were the best Mormons they could be and had a bunch of children. And only those who get to the highest level of THAT heaven get to work towards godhood.
Well, there’s one problem—actually, there are many problems—with that belief. You see, in Hebrews 9:27

One last thing real quick. There’s the whole issue of “baptism for the dead”. How you're supposed to go back through your family tree, and if you find people who weren’t Mormons, you're supposed to have somebody dunk you in water, and somehow that gets them into a better heaven. Er, something. They base this on 1st Corinthians 15:29

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References
(1) Ensign. 1986. pp. 25-26. link.
(2) TPJS. p. 349. link.
(3) Doctrine of Exaltation, or Becoming a God. From Partakers of the Divine Nature. Jordan Vajda. pp. 27-40. link.
(4) Encyclopedia of Mormonism. p. 485.
(5) The Teachings of Ezra Taft Benson. p. 7.
(6) First Presidency and Council of Twelve, 1916. Cited in Ensign. April 2002. p.13. link.
(7) Joseph Smith. King Follett Discourse. Mormon literature database—Brigham Young University. link.