Jacob's conclusion reprises the salvation theme of the prior day's sermon. These points have not been explicit in the current sermon, but are an essential part of the call to God. He closes, fittingly, on the mission of the coming Messiah.
Epigraph - Text and Context: What can we now discern of Jacob and his sermon? The major context is explained as a festival with a covenant-making sermon as might be fitting in such an occasion. That however, provides the excuse for the covenant speech and its gross outline. In the case of Jacob's text what is the context that makes it significant? The specific assignation of the Isaiah text by Nephi as the foundation of the sermon must be the significant clue. In that underlying textual theme, the salvation by Gentiles becomes relevant only in a social context placing the Nephites in a community with newly accepted Gentile members. The covenant renewal is therefore initiating the Gentiles into the community as well as reminding the Old World Nephites of their responsibility to accept theme - complete with prophetic theological justification.
The final context for the sermon is probably the frequent skirmishes that were noted with the Lamanites. Armed conflict with both Jews and Gentiles is a fact of life for the Nephite community (refer to verse 16). In that scenario, it may also be that the discourse on resurrection and everlasting life also had a very powerful and present context. It may be that the cost in human life, and the potential cost in human life also required a comforting sermon on the effect of their covenants on life after death.