Mormon combines his statements in verses 3 and 4, summarizing them here as the instruction to “come to the knowledge of your fathers.” One of the Book of Mormon’s functions is to show the remnant who their fathers were. Mormon’s record includes portraits of eminently admirable “fathers” but also some who were less than admirable.
The next message is, predictably, repentance, but he stresses that repentance must lead to an understanding of Yahweh-Messiah. Mormon is seeing his remnant audience as future Lamanite/Gadiantons; if they follow that model, then they have rejected the Savior in favor of other gods. The central message of the Book of Mormon has always been the Atoning Messiah. The future remnant must also come to know him.