Jacob hopes that the posterity of his people will read the words which he and others have written upon plates, and that they will "look upon them that they may learn with joy and not with sorrow, neither with contempt, concerning their first parents" (v. 3). Who are the first parents here? Possibly Lehi and Sariah. But why would Jacob worry that his grandchildren and great grandchildren would hold Lehi and Sariah in contempt? One possibility is that the Lamanites had a different version of history than the Nephites, and that the Lamanite version placed Lehi, Sariah, Nephi, Jacob and other righteous leaders in a less-than-favorable light.
It may also be possible that Jacob was concerned that his people wouldn’t understand the purpose of their mortal condition and that they would look disfavorably upon Adam and Eve—the first parents of the human family. As a temple priest, Jacob would have been keenly aware of the creation story, the Fall of Adam and Eve, and the introduction of the law of sacrifice. These are things that were essential to the temple in Israel, the tabernacle in the wilderness, and the ordinances and rituals over which Jacob would have been responsible.
Moreover, Jacob probably knew a more accurate story of Adam and Eve than is found in Genesis. I say this because there is good evidence that some of the things in the Book of Mormon are also found in the Book of Moses but not in the Book of Genesis. For instance, Lehi’s blessing upon Jacob includes information about the necessity of the Fall, stating that "Adam fell that men might be; and men are, that they might have joy (2 Nephi 2:25). This seems to echo Adam’s words in Moses 5:10 ("Blessed be the name of God, for because of my transgression my eyes are opened, and in this life I shall have joy") and also Eve’s words in Moses 5:11 ("Were it not for our transgression we never should have had seed, and never should have known good and evil, and the joy of our redemption").
It is thus possible that Jacob was trying to help his posterity better understand the purpose and necessity of mortality and that Lehi and Sariah, just like Adam and Eve, willingly chose to leave their comfortable home and embark on a journey through the wilderness—or, in other words, through a lone and dreary world. Jacob, who was Lehi’s "firstborn in the days of [his] tribulation in the wilderness," knew very well that "afflictions" and "sorrow" were a necessary part of mortal life and that the Lord can ultimately "consecrate thine afflictions for thy gain" (2 Nephi 2:1–2). There is no need to condemn our first parents when the power of Christ can transform our sorrows and afflictions into joy and into opportunities for spiritual growth and understanding.