In Deuteronomy 28:64 there is a prophecy about the House of Israel being scattered:
And the shall scatter thee among all people, from the one end of the earth even unto the other; and there thou shalt serve other gods, which neither thou nor thy fathers have known, wood and stone.
In their scattered state, the Lord wanted to gather them to Him. But they could be so stubborn. We see this in 3 Nephi 10:5:
And again, how oft would I have gathered you as a hen gathereth her chickens under her wings, yea, O ye people of the house of Israel, who have fallen; yea, O ye people of the house of Israel, ye that dwell at Jerusalem, as ye that have fallen; yea, how oft would I have gathered you as a hen gathereth her chickens, and ye would not.
But the Lord had made a covenant with His people that He would remember them,as we see in 2 Nephi 29:14:
And it shall come to pass that my people, which are of the house of Israel, shall be gathered home unto the lands of their possessions; and my word also shall be gathered in one. And I will show unto them that fight against my word and against my people, who are of the house of Israel, that I am God, and that I covenanted with Abraham that I would remember his seed forever.
And also in Jeremiah 23:3:
And I will gather the remnant of my flock out of all countries whither I have driven them, and will bring them again to their folds; and they shall be fruitful and increase.
And the promise is now coming true. In 1836, after the Kirtland Temple was dedicated, Joseph Smith and Oliver Cowdery experienced this vision as recorded in Doctrine & Covenants 110:11:
After this vision closed, the heavens were again opened unto us; and Moses appeared before us, and committed unto us the keys of the gathering of Israel from the four parts of the earth, and the leading of the ten tribes from the land of the north.
From these scriptures I have had impressed on me during my life that doing my part to gather Israel is not simply my duty as a member of the Church--it is helping the Lord fulfill a promise He made to His children.