This is he. — The words are those of the Evangelist, not of the Baptist, though the latter also used them to describe his own office (John 1:23). In each case the reference shows how strongly the great second part of Isaiah had impressed itself on the minds of men. To the Baptist, brooding over the sins of his people, and the long-expected consolation of Israel, there had come “the word of the Lord” (Luke 3:2), bidding him identify himself with that “voice of one crying in the wilderness.”
Historically, the connection of the opening Chapter s of this part of Isaiah with the protests against idolatry (Isaiah 40:18-24; Isaiah 41:7; Isaiah 44:9-20), and with the name of Cyrus (Isaiah 44:28; Isaiah 45:1), shows that the prophet blended his glorious visions of the ideal polity of the future with the return of the exiles from Babylon. The return came, and the ideal was not realised. The kingdom of heaven seemed still far off. Now, the Baptist came to proclaim its nearness.
Prepare ye the way of the Lord. — The imagery is drawn from the great strategical works of the conquerors of the East. They sent a herald before them to call the people of the countries through which they marched to prepare for their approach. A “king’s highway” had to be carried through the open land of the wilderness, valleys filled up, and hills levelled (the words used are, of course, poetical in their greatness), winding bye-paths straightened, for the march of the great army. Interpreted in its spiritual application, the wilderness was the world lying in evil, and the making low the mountains and hills was the bringing down of spiritual pride. When the poor in spirit were received into the kingdom of heaven, the valleys were exalted; when soldier and publican renounced their special sins, the rough places were made plain and the crooked straight.
It is probable that the stress thus laid upon “the way of the Lord,” in the first stage of the Gospel, led to the peculiar use of the term “the way” by St. Luke, to denote what we should call the “religion” of the Apostolic Church (Acts 9:2; Acts 18:25-26; Acts 19:9; Acts 19:23; Acts 22:4; Acts 24:14; Acts 24:22).