Literature: “This thing” refers to preservation of Jacob’s and Nephi’s record for his posterity and for the Lamanites. There are elements of parallelism and chiasm in this two-verse set, but if the original contained a polished chiasm, it has not been well preserved in English. Still, the two elements of posterity and Lamanites are given in reverse order and the theme of joy appears as the pivotal meaning. The “parents” is a repeated element, but it is directly rather than inversely parallel. Directly paralleled sets typically have a reinforcing function, which this set of lines lack.
Furthermore, because they are part of the aside, these lines seem to have been composed and inscribed simultaneously. I would expect more formal structures in a more planned setting. However, these parallels and reversals suggest that Jacob found this structure for presenting ideas natural, relying on them even in the absence of larger or more formal literary structures.