The passage is part of a messianic prophecy which declares that valleys shall be lifted up and hills made low; the rugged shall be made level and the rough places a plain (Isa. 40:4).
The lyrical beauty of the words is unique. The ups and downs of nature being made level cannot mean, though, that the physical structure of the universe will change in messianic times. Maimonides insists that we understand that hills will be hills, valleys will be valleys, people will be people and animals will be animals. That is not going to change.
The vision is of ethical, not physical levelling. It is already found in the second chapter of Isaiah with its reference to swords becoming ploughshares, and spears becoming pruning hooks.
In a just society there will be no jagged edges like swords and spears. All will be serene, and justice will be everywhere. The lowly, disadvantaged human beings who are like valleys will be raised up, and the high and mighty (the “mountains and hills”) will be cut down to size.
People will not have too much status or too little, too many material possessions or two few. Society will settle into equilibrium and there will be neither conflict nor contest, neither arrogance nor aggressiveness.
Hasten the day!