Commentary - Isaiah 40:3-5

Bird's-eye view

After the heavy judgments and pronouncements of the first thirty nine chapters, Isaiah 40 opens with a word of immense comfort. The warfare is over, the iniquity is pardoned (v. 2). And how is this comfort to be announced and brought into reality? It is through a preparatory work, a divine announcement that kicks off the greatest civil engineering project in human history. This is not a project of asphalt and gravel, but one of spiritual transformation. A voice cries out, heralding the coming of Yahweh Himself. This is the overture to the gospel. The New Testament writers leave us in no doubt as to the meaning of this passage. All four gospels point to John the Baptist as this crying voice, the forerunner who prepared the way for Jesus Christ (Matt. 3:3; Mark 1:3; Luke 3:4; John 1:23). But the fulfillment is not a simple one-and-done event. John prepared the way for Christ's first coming, and the Church, by the preaching of the gospel, continues this road work, preparing the way for His ultimate and final triumph over all the earth.

What Isaiah describes here is nothing less than the reordering of the world to make way for the glory of God. The wilderness, a symbol of desolation, sin, and separation from God, is to become a superhighway for our God. The very topography of the fallen world, with its proud mountains of human arrogance and its deep valleys of despair, is to be leveled. This is the work of the gospel. It brings low the proud and lifts up the humble. The end result is that the glory of Yahweh will be revealed, and this is not a private vision for a select few. All flesh, together, will see it. This is a public, global, historical unveiling of the majesty of God in the person and work of His Son. And the guarantee of this staggering promise is as firm as it gets: "For the mouth of Yahweh has spoken."

Outline

Clause-by-Clause Commentary

v. 3 A voice is calling, “Prepare the way for Yahweh in the wilderness; Make smooth in the desert a highway for our God.

The chapter begins with comfort, and that comfort is delivered by a voice. It is an anonymous voice at this point, but it is a voice with authority, a herald's cry. This is the announcement that something stupendous is about to happen. God is on the move. And when God is on the move, preparations must be made. The location is significant, "in the wilderness." The wilderness in Scripture is a place of testing, of chaos, of sin, and of death. It is where Israel wandered; it is where Jesus was tempted. It is the perfect picture of a world alienated from God. And it is precisely into this desolation that the work of preparation must begin.

The task is defined as preparing "the way for Yahweh." This is royal language. When a great king was to visit a province, roads were cleared, potholes were filled, and the way was made straight for his entourage. Here, the King is Yahweh Himself. The work is to "make smooth in the desert a highway for our God." This is not about literal road construction. This is a profound metaphor for repentance. Preparing the way for God means dealing with the sin that makes the terrain of our hearts and cultures impassable for His glorious presence. It is the work of turning from our crooked ways, our self-reliance, our idolatries, and making a straight path for Him to come, not just into our individual lives, but into the world. John the Baptist understood this perfectly. His message was simple and direct: "Repent, for the kingdom of heaven is at hand" (Matt. 3:2). Repentance is the bulldozer and the grader for this divine highway.

v. 4 Let every valley be lifted up, And every mountain and hill be made low; And let the rough ground become a plain, And the rugged terrain a broad valley;

Here Isaiah elaborates on the nature of this spiritual earth-moving. The imagery is cosmic in its scope. "Every valley be lifted up." Think of the valleys of despair, hopelessness, poverty, and oppression. Think of the downcast and the humble, those who have been crushed by the world. The gospel comes to them as a lifting up, an exaltation. The poor in spirit are blessed, for theirs is the kingdom of heaven (Matt. 5:3). God fills the hungry with good things (Luke 1:53). This is the great reversal of the gospel.

Conversely, "every mountain and hill be made low." The mountains and hills represent human pride, arrogance, and self-sufficiency. They are the towers of Babel we construct, the institutions of rebellion, the philosophies that exalt man against God. The gospel comes with a sledgehammer for these high places. God opposes the proud but gives grace to the humble (James 4:6). The coming of Christ is a judgment on all human pretension. Every system that sets itself up as a rival to God, whether it is a tyrannical state, a secular university, or the pride in our own hearts, will be brought low. The "rough ground" of our complicated sins and excuses will be made a plain, and the "rugged terrain" of our rebellious wills will become a broad, open valley, ready for the King's arrival.

v. 5 Then the glory of Yahweh will be revealed, And all flesh will see it together; For the mouth of Yahweh has spoken.”

This is the goal of the whole enterprise. The preparation is not an end in itself. The road is built so that the King can travel on it. And when He comes, He brings His glory with Him. "Then the glory of Yahweh will be revealed." The glory of God is the visible manifestation of His supreme excellence and worth. In the Old Testament, it was seen in the cloud and fire, and it filled the tabernacle. But the ultimate revelation of that glory was in the person of Jesus Christ. "And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth" (John 1:14).

And this revelation is not a secret. It is not for a small group of mystics. The promise is that "all flesh will see it together." This is a public, historical, global event. This points to the first coming of Christ, certainly, where His glory was revealed to Israel. But the scope of "all flesh" pushes us forward. This is a thoroughly postmillennial promise. It speaks of the day when the knowledge of the glory of the Lord will cover the earth as the waters cover the sea (Hab. 2:14). The gospel highway is being extended to every nation, tribe, and tongue. And as that road is built through the faithful preaching of the Word, the glory of God in the face of Christ is revealed more and more brightly, until that final day when every eye will see Him.

How can we be sure of such a grand and seemingly impossible outcome? The final clause provides the bedrock foundation: "For the mouth of Yahweh has spoken." This is not the speculation of a prophet. This is not a hopeful wish. This is the declared purpose of the sovereign God who speaks and brings worlds into being. His word does not return to Him void but accomplishes the purpose for which He sent it (Isa. 55:11). The transformation of the entire world into a theater for His glory is as certain as His own existence. He has spoken it, and therefore it will be done.

Application

The application of this text is both personal and cosmic. First, we must ask ourselves if the roadwork has begun in our own hearts. Are there proud mountains of self-righteousness that need to be brought low? Are there valleys of unbelief or despair that need to be filled in with the promises of God? We are called to be personal road-builders, continually preparing the way of the Lord in our own lives through repentance and faith.

But we must not stop there. This passage is a great missionary and cultural text. The church is God's road crew in the world today. Through the preaching of the gospel, the administration of the sacraments, and the discipleship of the nations, we are leveling the mountains and raising the valleys. We are making a highway for our God in the wilderness of our pagan culture. This is not a call to retreat into a holy huddle, but to engage in the world with the transforming power of the gospel. We do this work with great confidence, not because our tools are so great or our efforts so mighty, but because the mouth of Yahweh has spoken. The glory of the Lord will be revealed, and all flesh shall see it together. Our job is to get our shovels and get to work.