In Isaiah, chapter forty, verses three through eight have much prophecy, and have several levels of application: to God’s people, restoration from exile, to the coming of the Messiah and His salvation, and to the consummation of redemption in the new heaven and the new earth. The New Testament sees the fulfillment of verse three in John the Baptist, “The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God.” He is the forerunner of the Messiah, as in Matthew three, verses one to four, Mark one, verses one through four, Luke one, verses seventy-six to seventy-eight, and John one, verse twenty-three, respectively. John made clear that the way to prepare for the Lord’s coming was through repentance, as in Matthew three, verses one to eight.
The remaining theme verses, “Every valley shall be exalted, and every mountain and hill shall be made low: and the crooked shall be made straight, and the rough places plain: And the glory of the LORD shall be revealed, and all flesh shall see it together: for the mouth of the LORD hath spoken it. The voice said, Cry. And he said, What shall I cry? All flesh is grass, and all the goodliness thereof is as the flower of the field: The grass withereth, the flower fadeth: because the spirit of the LORD bloweth upon it: surely the people is grass. The grass withereth, the flower fadeth: but the word of our God shall stand for ever.”
The passage is memorable and deliberately taken by the Baptist as defining his mission. The wilderness is between the Euphrates and Judah, the journey of the exiles through it reminding the prophet of the older wanderings in the wilderness of Sin.