These scriptures all deal with the antemortal existence of man. Notice The Book of Mormon references.
So, I beg to differ when it is said that it doesn't mention it. I put them in a pretty purple color.
Num. 16: 22(
Num. 27: 16) God of the
spirits of all flesh.
Job 38: 7all the
sons of God shouted for joy.
Eccl. 12: 7the
spirit shall return unto God who gave it.
Jer. 1: 5Before I
formed thee in the belly I knew thee.
Zech. 12: 1Lord . . . formeth the
spirit of man within him.
John 9: 2who did sin, this
man, or his parents, that he was born blind.
Acts 17: 28poets have said, For we are also his
offspring.
Rom. 8: 29For whom he did
foreknow, he also did predestinate.
Eph. 1: 4chosen us in him
before the foundation of the world.
Heb. 12: 9subjection unto the Father of
spirits.
Jude 1: 6angels which kept not their
first estate.
Rev. 12: 7Michael and his angels fought against the dragon.
Alma 13: 3called and prepared from the foundation of the world. Hel. 14: 17bringeth mankind . . . back into the presence of the Lord. D&C 29: 36third part of the
hosts of heaven turned he away.
D&C 38: 1seraphic hosts of heaven,
before the world was made.
D&C 49: 17man, according to his creation
before the world.
D&C 93: 29Man was also in the
beginning with God.
D&C 138: 53choice
spirits who were reserved to come forth.
D&C 138: 56before they were born . . . received their first lessons.
Moses 3: 5in heaven
created I them, and there was not yet flesh upon the earth.
Moses 6: 36he beheld the
spirits that God had created.
Abr. 3: 22intelligences that were organized before the world was.
Abr. 3: 23he stood among those that were
spirits.
Abr. 5: 7took his
spirit . . . and put it into him.