[to the Gentiles who have care for the house of Israel]: This is an interesting phrase because it describes a relationship between Israel and the Gentiles that has no obvious antecedent. Mormon is citing this information rather quickly, and without explanation, therefore assuming that it is something that we ought to know. Mormon is referencing scripture, and he is referencing passages in Isaiah that we have see twice before, but only in the holographic text of Nephi, son of Lehi (see 1 Nephi 21:22-23 , and 2 Nephi 6:6-7). The reference is:
Isaiah 49:22-23
22 Thus saith the Lord GOD, Behold, I will lift up mine hand to the Gentiles, and set up my standard to the people: and they shall bring thy sons in their arms, and thy daughters shall be carried upon their shoulders.
23 And kings shall be thy nursing fathers, and their queens thy nursing mothers: they shall bow down to thee with their face toward the earth, and lick up the dust of thy feet; and thou shalt know that I am the LORD: for they shall not be ashamed that wait for me.
These are the only verses in our current Book of Mormon that clearly position the Gentiles as the protectors of Israel. The discourse of the Savior during his visit explains the role of the Gentiles in bringing for the gospel and the Book of Mormon, but never describes them as protectors. Only in this passage do we find the Gentiles in such a position relative to Israel.