Jacob makes certain that his audience has understood the reason for the quotations from Isaiah. Jehovah is their god. For some, Jehovah was a new god. Thus, it is important to understand that Jehovah has a covenant with the house of Israel. This is not a distant and capricious god who must be cajoled into helping humankind, this is the Lord of Hosts who has covenanted to help Israel, and whose covenants He does not abandon.
Thus, for Jacob’s audience, he speaks these things that they may rejoice, that they may know that they are included in the covenant with Jehovah, and therefore the protection of the covenant is upon them. This is the Jehovah who covenanted with the children of Lehi, and specifically with Nephi, that they would prosper in this land if they obeyed Jehovah’s law, of which Isaiah had spoken.