Mormon is addressing the Gentiles who are the protectors of Israel, and those who “realize and know from whence their blessings come.” (verse 10).
These Gentiles will be the ones who will recognize the true state of the house of Israel and understand their sorrow rather than condemn them. The contrast between types of Gentiles was part of the Savior’s message that Mormon recorded:
3 Nephi 16:6-9
6 And blessed are the Gentiles, because of their belief in me, in and of the Holy Ghost, which witnesses unto them of me and of the Father.
7 Behold, because of their belief in me, saith the Father, and because of the unbelief of you, O house of Israel, in the latter day shall the truth come unto the Gentiles, that the fulness of these things shall be made known unto them.
8 But wo, saith the Father, unto the unbelieving of the Gentiles—for notwithstanding they have come forth upon the face of this land, and have scattered my people who are of the house of Israel; and my people who are of the house of Israel have been cast out from among them, and have been trodden under feet by them;
9 And because of the mercies of the Father unto the Gentiles, and also the judgments of the Father upon my people who are of the house of Israel, verily, verily, I say unto you, that after all this, and I have caused my people who are of the house of Israel to be smitten, and to be afflicted, and to be slain, and to be cast out from among them, and to become hated by them, and to become a hiss and a byword among them—
The Gentiles who are true believers will support truth and Israel in the latter days. The Gentiles who are not will consider Israel a “hiss and a byword.”