When people prepare the road for an important person who is coming, they cut down the high places and fill in the low places so that the road will be level. This is part of the metaphor started in the previous verse. (See: [[rc://en/ta/man/translate/figs-metaphor]])
This can be stated in active form. AT: "they will level every mountain and hill" or "they will remove every high place in the road" (See: [[rc://en/ta/man/translate/figs-activepassive]])