Isaiah turns from prophesy to exultation. While there might be difficulties along the way, the final state is to be joyful. Isaiah poetically anthropomorphizes the land of Judah and has the mountains sing. The singing is that they “shall be smitten no more, for the Lord hath comforted his people, and will have mercy upon his afflicted.”
The Assyrian invasion scattered the ten tribes, and Lehi had prophesied that Babylon would also drive out those of Jerusalem. The children of Israel certainly knew afflictions in the Old World. Nephi began writing on the small plates some thirty years after the family left Jerusalem. By the time forty years had passed, Nephi could say that “we had already had wars and contentions with our brethren” (2 Nephi 5:34). If some of those contentions happened before Nephi recorded this chapter from Isaiah, it would have resonated with the promise that the children of Israel would be “smitten no more.” Even if it had not yet happened, he knew that it would, based on his vision of the future of his people that he had during the vision of the Tree of Life.
The difficulties would make Zion lament that Jehovah had forsaken them. Isaiah has Jehovah rebuke that sentiment. Jehovah asks if a mother can forget her young child. It would be obvious that such a thought would have been unthinkable. So too must Jehovah remember his own children. For Nephi, that included his people who were scattered to an isle of the sea.