The earth and all its inhabitants, save eight, were once destroyed by water. When the Lord comes again, the wicked will again be destroyed—this time by fire. Hereby the earth is baptized both by water and by fire. When the scripture says the day cometh that shall burn as an oven, this is not figurative but literal, for the wicked will be burned, every corruptible thing, both of man, or of the beasts of the field, or of the fowls of the heavens, or of the fish of the sea, that dwells upon all the face of the earth, shall be consumed; And also that of element shall melt with fervent heat; and all things shall become new, that my knowledge and glory may dwell upon all the earth (DC 101:24-25).
The keys to avoid this burning are tithing and temple work, Behold, now it is called today until the coming of the Son of Man, and verily it is a day of sacrifice, and a day for the tithing of my people; for he that is tithed shall not be burned at his coming. For after today cometh the burning (DC 64:23-24).
Joseph Smith
“How shall God come to the rescue of this generation? He will send Elijah the prophet…In the days of Noah, God destroyed the world by a flood, and He has promised to destroy it by fire in the last days: but before it should take place, Elijah should first come and turn the hearts of the fathers to the children...” (Teachings, p. 323, 337)