One of Nephi’s purposes in his expansion and interaction with the Isaiah chapters is to return to his vision that he received of the tree of life. That vision included scenes of the future, and Nephi is using Isaiah to expand and support his understanding of that vision of the future.
At this point, however, he returns specifically to the vision and his own descriptions, rather than interact with Isaiah. When Nephi mentioned the future churches in the previous verses, his intent was to place them as antithetical to God’s true way. This is Nephi’s definition of the great and abominable church. It is not a specific church, but a symbolic church that is the opposite of God’s church.
In the last days, there will be an accounting. Isaiah’s vision of the last days has a triumphant Messiah establishing his rule over all the nations. Nephi’s emphasis is not on the militaristic Messiah, but on the atoning Messiah. Nephi’s emphasis for the final days is the victory of the gospel, not the victory of nations.