Isaiah 40:3

"The voice of one that crieth, Prepare ye in the wilderness the way of Jehovah; make level in the desert a highway for our God. Every valley shall be exalted, and every mountain and hill shall be made low; and the uneven shall be made level, and the rough place a plain: and the glory of Jehovah shall be revealed, and all flesh shall see it together; for the mouth of Jehovah hath spoken it."

The first impression here may be that God will precede the captives on the way back home from Babylon, and that these words are a call to prepare the Lord's way through the desert. However, as Archer noted:

"From Matthew's application of this verse to the ministry of John the Baptist (Matthew 3:3), it is apparent that these geographical features symbolize the arid lifelessness of the unconverted soul. The hills represent the carnal pride of the sinner, the valleys his moods of carnal hopelessness and self-pity."[5]

In short, the meaning is that Judah should prepare their hearts for the coming manifestation of God in their deliverance.

The figure of leveling and preparing literal roads is taken from the practice of some ancient rulers who actually required such preparation when they traveled to distant places. An ancient example of this, given by Lowth, is seen in the march of Semaramis' marches into Media and Persia, "She ordered the precipices to be digged clown and the hollows to be filled up; and, at great expense, she made a shorter and more expeditious road."[6]

Despite the obvious primary application of this passage to the return of Israel from the Babylonian captivity, "At the same time it is clear that the prophet was inspired to use language of a special design that should also appropriately express an even more important event, the coming of John the Baptist, the forerunner of the Messiah, and the work that he would perform as preparatory to the first advent of Messiah."[7]

As Adam Clarke noted, "We have the irrefragable authority of John the Baptist and of our blessed Saviour himself, as reported by the gospels, that these verses apply to the introduction of the Gospel and the kingdom of Christ, who was to effect a much greater deliverance of God's people, Jews and Gentiles alike, from the captivity of sin and the dominion of death."[8]