In Isaiah 2:2, it says:
“And it shall come to pass in the last days, that the mountain of the Lord’s house shall be established in the top of the mountains, and shall be exalted above the hills; and all nations shall flow unto it.”
(This verse is also in 2 Nephi 12:2) The ‘mountain of the Lord’s house’ is the temple. While one is performing ordinances in the temple, one follows a path upwards, like climbing, or ascending, a mountain. This notion describes our journey as we ascend towards God.
In his vision, Isaiah saw the temple in the mountains, and it just so happens that the LDS Temple in Salt Lake City is in the mountains! So, Isaiah was prophesying of the establishment of the LDS Temple in Salt Lake City!
This is what I previously wrote after reading 2 Nephi 12: We’re Back!