[also that a knowledge of these things must come unto the remnant of these people]: Mormon understands that he is writing for a future audience. He had no hope that he could save his contemporaneous people, but he does have hope that he can save the future remnant of that same people. At this point where he sees the current failure, he turns more fervently to the possible future success.
Textual: Mormon tells us rather certainly that he is writing an abridgement at the time he is describing. Therefore he was in the process of writing during the three hundred and eightieth year, or when he as nearly 70 years old. We cannot tell where he was in the creation of the abridgement, but we can be certain that at this year he was in the process of writing it.