3 Nephi 21

As the Lord continues to teach the people of the Americas, He prophecies -

"..I give unto you a sign, that ye may know the time when these things shall be about to take place—that I shall gather in, from their long dispersion, my people, O house of Israel, and shall establish again among them my Zion;
2 And behold, this is the thing which I will give unto you for a sign—for verily I say unto you that when these things which I declare unto you, and which I shall declare unto you hereafter of myself, and by the power of the Holy Ghost which shall be given unto you of the Father, shall be made known unto the Gentiles that they may know concerning this people who are a remnant of the house of Jacob, and concerning this my people who shall be scattered by them..." (Book of Mormon | 3 Nephi 21:1 - 2)

And -

"...when these things shall be made known unto them of the Father, and shall come forth of the Father, from them unto you; 4 For it is wisdom in the Father that they should be established in this land, and be set up as a free people by the power of the Father, that these things might come forth from them unto a remnant of your seed, that the covenant of the Father may be fulfilled which he hath covenanted with his people, O house of Israel..." (Book of Mormon | 3 Nephi 21:3 - 4)

It is the coming forth of the Book of Mormon that is the sign that the covenants of the Father prophesied by Old Testament prophets (especially Isaiah)are being fulfilled. And that it was essential that this land be a land of freedom for that to take place. In other words, the Lord's hand was involved with this country becoming a land of the free. I would suggest anyone that takes away from that is rebelling against the will of God. It is in these teachings the Savior provides many warnings and prophecies. But that which I feel to be most important is -

"...it behooveth the Father that it should come forth from the Gentiles, that he may show forth his power unto the Gentiles, for this cause that the Gentiles, if they will not harden their hearts, that they may repent and come unto me and be baptized in my name and know of the true points of my doctrine, that they may be numbered among my people, O house of Israel..." (Book of Mormon | 3 Nephi 21:6)

The house of Israel will eventually be the sons and daughters of God, His eternal and exalted family. And the warning is -

"...that at that day whosoever will not repent and come unto my Beloved Son, them will I cut off from among my people, O house of Israel..." (Book of Mormon | 3 Nephi 21:20)

Even though the wicked will be destroyed at His coming, the greatest loss will be being cut off from the house of Israel forever. I believe the gathering spoken of is more related to the spiritual gathering are becoming chosen to be part of the house of Israel than a physical gathering.