Mormon combines the first two statements into the foundation of this one. The future remnant must first come to a knowledge of their fathers. That is one of the functions of the Book of Mormon, to show to the remnant who their fathers were. As Mormon has painted a picture of those fathers he has given several who are eminently admirable. He has also not declined to paint a picture of those who were less than admirable. He desires that the future remnant really known and understand their fathers.
Of course the next message is repentance, but particular a repentance that will lead to an understanding of Jesus Christ. This is an important part of his message for his mental picture of who that remnant was. If Mormon is seeing them as future Lamanite/Gadiantons, then he understands that the future remnant, like the current Lamanites, have rejected the Savior in favor of other Gods. The message of the Book of Mormon has always been the centrality of the Atoning Messiah, known as Jesus. The future remnant must also come to know their Atoning Messiah.