Jacob's introduction to mercy begins with a set of people to whom that mercy has been extended. The righteous will be those who will inherit the kingdom of God. Note that by using the righteous as an example he uses those who will have righteously judged themselves. There would be little question of their deserving status. Nevertheless, Jacob makes it clear that their presence is not simply due to the justice of God, but also to his mercy.
Textual analysis: The phrase "endured the crosses of the world" appears somewhat anachronistic in a pre-crucifixion setting. The idea of crucifixion would not be one that was carried into the new world, and while Nephi (and possibly Jacob's) vision might have show the mode of Christ's death, it may be a little much to presume that it became a widespread phrase sufficient for the purposes of this text in such a short time. This may be best explained as a transference of meaning rather than a direct translation of words on the plates.