A voice is calling, “Clear the way for the LORD in the wilderness; Make smooth in the desert a highway for our God”. (Isaiah 40:3)
A prophetic exhortation told Israel to prepare for the revelation of the Lord’s glory at the arrival of Messiah. Scripture sees John the Baptist in this role. It likewise sees the future forerunner who is to be like Elijah preparing for Christ’s second coming.
Prepare the way. The remnant of Israel could remove obstacles from the coming Messiah’s path through repentance from their sins. John the Baptist reminded his listeners of this necessity as did Jesus.
The verses in Isaiah 40:3-5 reflect the custom of some eastern monarchs to send heralds before them to clear away obstacles, make causeways, straighten crooked roads and valleys, and level hills. John had the task of getting people ready for Messiah’s arrival. (Commentary by John MacArthur)