It is difficult to imagine a human being contemplating a more dismal prospect for the future than that which confronted Mormon at this particular time. He had witnessed the end of the entire Nephite civilization and the closing of an epic in American history which had been a horrible and terrifying experience. Mormon therefore decided to focus his attention on the distant future. There, at least, one might find a measure of hope.
Notice that he is going to address the "remnants of this people." This remnant would be a mixture of Lamanites, Nephites and Mulekites, but he wants them to remember that regardless of their various branches, they are all children of Israel.