According to Douglas and Robert Clark, perhaps the most conspicuous aspect of Jacob's preaching in comparison with the rest of the Book of Mormon is his constantly repeated designation of God as "the Holy One of Israel" (2 Nephi 6:9). That this title would surface somewhere in Jacob's preaching about Isaiah is no surprise, of course, since the title occurs in the Old Testament primarily in Isaiah but only infrequently elsewhere (usually in dependent passages). . . . Moreover, his brother Nephi (see 1 Nephi 19:14-15) and their father, Lehi (see 2 Nephi 1:10; 3:2) had already used the title in speaking of God. Even so, Jacob's usage of the title stands out for two reasons:
1. The particular Isaiah passage he quotes never expressly uses the title; and
2. Jacob uses the title far more frequently (some seventeen times in just two chapters -- 2 Nephi 6 and 9) than any other primary Book of Mormon writer does elsewhere in the rest of the book. (Nephi uses it in his own writing some twelve times (1 Nephi 19:14-15; 22:5,18,21,24,26,28; 2 Nephi 25:29; 28:5; 30:2; 31:13); and Amaleki uses it twice (Omni 1:25-26). The title also appears some seven times in Isaiah passages quoted in the Book of Mormon.)
Why, then, does Jacob draw so frequently on the title "the Holy One of Israel"? The answer at least in part could be because of his own heightened awareness of and identification with his ancient namesake, the patriarch Jacob (Israel), and the covenants he had received. This could also explain Jacob's continued obsession (once Nephi turned the sacred record over to him) with the destiny of the house of Israel: nearly one-third of Jacob's own writing (in the book of Jacob) is devoted to reproducing the lengthy and elaborate allegory by the prophet Zenos comparing the house of Israel to an olive-tree (see Jacob 5). [E. Douglas Clark and Robert S. Clark, Fathers and Sons in the Book of Mormon, pp. 35-36]