Nephi is quoting “the prophet” which seems to be a continuation of his quoting Isaiah. However, the text does not specify who Nephi is quoting. Another possibility is that he is quoting Zenos. Nephi had earlier referred repeatedly to Zenos as “the prophet” (1 Nephi 19: 10–17). Elder Bruce R. McConkie called him:
Some unnamed Old Testament prophet, who obviously was Zenos, as the Book of Mormon testifies, spoke of the day when the wicked would be destroyed as stubble; when the righteous would be “led up as calves of the stall;” when Christ should “rise from the dead, with healing in his wings;” and when the Holy One of Israel would then reign on earth.
Malachi, who lived more than two hundred years after Nephi, uses these very expressions in his prophetic writings. Can we do other than conclude that both Nephi and Malachi had before them the writings of Zenos (or Isaiah)?
The time period spoken of by “the Prophet” is definitely the Second Coming of Christ when the righteous will be preserved and the wicked destroyed. It is a continuation of Nephi’s interpretation of Isaiah 49:26, the great and abominable church warring among themselves. Since it is either Zenos or Isaiah speaking, it was not included in Nephi’s commentary on 1 Nephi 21:26.