In their fallen and mortal state, caused by their partaking of the fruit, Adam and Eve were able to have children, and thus became the first parents “of all the family of the earth” (v. 20; italics added). Wherefore, all the inhabitants of the earth are the descendants o f Adam and Eve.
To fulfill the will or plan of God, Lehi explains that the children of Adam, or all the people of the earth, had their days prolonged to live upon the earth. This provided them a probationary time, or a time to be tested, and a time to be able to repent of their wrong choices while living upon the earth. This time was needed because all men were lost (fallen) because of the transgressions of their parents, Adam and Eve (v. 21). The Lord told Adam: “Inasmuch as thy children are conceived in (a world of) sin, even so when they begin to grow up, sin conceiveth in their hearts, and they taste the bitter, that they know to prize the good” (Moses 6:55).
Lehi expounded on the purpose of the fall. Had there been no fall things would have remained constant (v. 22). Therefore there would have been no death. This doctrine, and other doctrines taught by Lehi, is confirmed in the Book of Moses. Enoch taught: “Because that Adam fell, we are; and by his fall came death; and we are made partakers of misery and woe,” and the Lord told Adam that the “fall bringeth death” (Moses 6:59).
Another factor of the Fall was the birth of children to Adam a nd Eve. Had there been no fall, “they would have had no children.” Remaining “in a state of innocence” (v. 19) implies that the process of creating children was not known. However, as stated above, Alma 12:22 teaches that “Adam did fall by the partaking of the forbidden fruit,” and Lehi records that children were born after they were driven out of the Garden of Eden (2:19–20). Although it says they “would” have had no children, the text supports they “could” have had no children, it being biologically impossible. Regardless, children were not born unto Adam and Eve until after the Fall. The Book of Moses does not say they could have had no children, but does sustain there being no children until after the Fall. After listening to Adam prophesying about the Fall, Eve said: “Were it not for our transgression we never should have had seed, and never should have known good and evil” (Moses 5:11).
The Fall was purposeful, and was “in the wisdom of him who knoweth all things. Adam fell that men might be; and men are, that they might have joy” (vv. 24–25). The Fall was to bring mortality, and men were placed on earth “to bring to pass the immortality and eternal life of man” (Moses 1:39). Man must receive a fullness of truth by keeping the commandments of God, die, and be resurrected, or “be inseparably connected [to] receive a fulness of joy” (D&C 93:27–28, 33). Joseph Smith gave us a similar teaching: “We came to this earth that we might have a body and present it pure before God in the celestial kingdom. The great principle of happiness consists in having a body” (TPJS, 181). Without the Atonement, we cannot be pure before God. Lehi now teaches us this doctrine.