I will be the first to tell you that I am not a Mormon. The article on your web site entitled, How to Use the Book of Mormon, is very good. But keep in mind, that a Mormon could challenge your article where it says that the Mormon doctrine of pre-existence is not found in the book of Mormon. You need be to adequately prepared for such an encounter. To do this, I recommend that you read the Mormon article entitled, "Does the Book of Mormon Teach Mormonism?" Have you read and studied this one? It is a 7-page article by Michael T. Griffith, Copyright 1992. At any rate, please give me the benefit of the doubt: I am trying to help you and not hinder you. I just thought I would mention it. Your web-site is a good one. Keep up the good work!
I read through the section on Pre-Mortal Life in the article you cited. I couldn't help but notice that he stated: "The doctrine of preexistence can be found in the Bible, in ancient Jewish sources, and in early Christian writings," but he offers no proof. Instead, he credits this statement to another Mormon writer.
I read through about the first ten of his proofs from the Book of Mormon. I was suspicious because he gave citings without any quotes. Every one that I read talks about salvation, redemption, a kingdom, and the like being prepared before the foundation of the world. None states that people existed before the foundation of the world. It is amazing that a Mormon will be this dishonest with the teachings of his own religion's writings.
Let me give you a few examples. These are the passages the author claims shows the pre-mortal existence, in other words the idea that people's spirits exist prior to conception.
1 Nephi 10:18
"For he is the same yesterday, today, and forever; and the way is prepared for all men from the foundation of the world, if it so be that they repent and come unto him."
What existed before the foundation of the world? "The way."
2 Nephi 9:18
"But, behold, the righteous, the saints of the Holy One of Israel, they who have believed in the Holy One of Israel, they who have endured the crosses of the world, and despised the shame of it, they shall inherit the kingdom of God, which was prepared for them from the foundation of the world, and their joy shall be full forever."
What existed from the foundation of the world? "The kingdom of God."
2 Nephi 27:10
"But the words which are sealed he shall not deliver, neither shall he deliver the book. For the book shall be sealed by the power of God, and the revelation which was sealed shall be kept in the book until the own due time of the Lord, that they may come forth; for behold, they reveal all things from the foundation of the world until the end thereof."
What existed from the foundation of the world? Actually, this verse just claims there is a book that reveals all things from the foundation of the world. It doesn't state that anything in particular existed that long.
"I say unto you, if ye have come to a knowledge of the goodness of God, and his matchless power, and his wisdom, and his patience, and his long-suffering towards the children of men; and also, the atonement which has been prepared from the foundation of the world, that thereby salvation might come to him that should put his trust in the Lord, and should be diligent in keeping his commandments, and continue in the faith even unto the end of his life, I mean the life of the mortal body — I say, that this is the man who receiveth salvation, through the atonement which was prepared from the foundation of the world for all mankind, which ever were since the fall of Adam, or who are, or who ever shall be, even unto the end of the world."
What existed from the foundation of the world? "Atonement."
"For were it not for the redemption which he hath made for his people, which was prepared form the foundation of the world, I say unto you, were it not for this, all mankind must have perished."
What existed from the foundation of the world? "Redemption."
I think you should see the pattern. The author simply did a word search on the phrase "foundation of the world" listed the verses and claimed this as proof that mortal man's spirit pre-exists without ever looking to see what these verses actually state is pre-existing.
Given the lack of quality in the author's reasoning in this one point, I didn't bother to read further.