In chapter 4, Jacob writes a few words to introduce his long quotation of Zenos’s Allegory of the Olive Tree. He says that he has "ministered much unto my people in word," realizing that verbal talk will be forgotten and can’t be remembered. And thus it is important for him, and all of us, to leave a written record. He admired the writings of Zenos, which set the example and had "remained."
Book of Mormon Central, "Why Did Book of Mormon Prophets Quote Long Passages of Scripture? (1 Nephi 19:22)," KnoWhy 473 (October 4, 2018).