Isaiah 40:5 Commentary: A Promise of Universal Revelation

Isaiah 40 opens the section often called Second Isaiah (chapters 40, 55), written to Judean exiles in Babylon around 540 BC. The Persian king Cyrus had not yet issued his decree, but the prophet sees its approach as certain. The surrounding verses paint a scene of comfort: Jerusalem’s “warfare is accomplished,” her iniquity pardoned (v.2). The highway through the wilderness (v.3, 4) is not a literal road but a poetic way for Yahweh to lead his people home, like a second exodus. In that ancient deliverance, God’s glory appeared as a pillar of cloud and fire; here the prophet promises an even greater unveiling.

The phrase “all flesh” is striking. In the Old Testament, “flesh” often connotes human frailty (Genesis 6:12, Psalm 145:21). By using it, the prophet includes Gentiles, a radical move for a people defined by the covenant. Later in the same book, God declares his servant will be “a light to the nations” (Isaiah 49:6). The return from exile was a local event, yet the language swells beyond it, hinting that God’s ultimate purpose is to show his glory to every nation. The final clause echoes other prophetic affirmations (Isaiah 1:20) and functions as a seal: what God has spoken, he will do.

The consulted sources note one significant variant. In the Septuagint, the verse reads “and all flesh shall see the salvation of God” (το σωτηριον του Θεου). The Hebrew text lacks the object “salvation,” and English translations supplied the word “it” to complete the sense. The Chaldee, Syriac, Vulgate, and all extant Hebrew manuscripts support the shorter reading. Luke 3:6, quoting Isaiah, includes “the salvation of God,” but may be drawing from Isaiah 52:10 rather than a variant text. Barnes and the Cambridge Bible judge that the Septuagint addition is not original to the Hebrew, though Clarke considers it genuine. No other textual issues are raised by the supplied sources.

In the New Testament, Luke directly applies this verse to John the Baptist’s ministry (Luke 3:4, 6), reading it as preparation for Christ. The early church saw the revelation of glory in the incarnation, crucifixion and resurrection. During the Middle Ages, the verse was used in Advent liturgies to look forward to both Christ’s first and second coming. Protestant Reformers like Calvin and Luther connected it to the preaching of the gospel that makes Christ visible in all nations. Modern evangelical preaching often cites it as a mission text: God’s glory is meant to be seen by every person. Jewish interpretation has traditionally connected the passage to the messianic era when God’s kingship will be universally acknowledged. The verse thus has served as a bridge between the historical hope of restoration and the Christian confession that in Jesus, God’s glory was fully revealed.

Three-point outline

1. The promise of glory. God’s “glory” (kabod) means his visible weight and majesty. He does not reveal it in a corner but in a public act of salvation, first in Babylon’s fall, finally in Christ’s cross and resurrection.
2. The universal scope. “All flesh” includes the weak, the foreign, the unexpected. The revelation is not exclusive to Israel; it is for everyone. This grounds the mission of the church.
3. The unshakable word. “The mouth of Yahweh has spoken it” is the prophet’s signature guarantee. God’s promise stands against human doubt. The grass withers, but this word stands forever (v.8).

Five-point outline

1. The context of comfort. The exiles are forgiven (v.2). God’s glory is good news, not threat.
2. The preparation. A way is made in the wilderness (v.3, 4). Obstacles are removed. God clears a path for his coming.
3. The revelation of glory. The Lord himself appears in power, showing he is the covenant-keeping God.
4. The universal witness. All flesh together sees, a shared, public event, not a private vision.
5. The certain word. The prophecy rests on God’s own speech, not human reasoning. It will happen.

Illustration hooks

• A city waits years for a promised rail line. When it finally opens, everyone turns out. The completion reveals the planners’ competence. God’s promise, long deferred, is kept with public display.
• A family separated by war is reunited at an airport. Neighbors and strangers watch the embrace. The joy is contagious and visible to all. God’s restoration of his people is that kind of public event.

Questions your congregation is asking

• “Is God still at work when I see only suffering and delay?”, The exile seemed endless, but God had a set time.
• “Does the gospel really reach people who never enter a church?”, “All flesh” includes those far off.
• “How can I trust a promise I don’t yet see?”, The mouth of the Lord has spoken it; his word outlasts grass.

This passage announces that God’s glory will be publicly visible to the whole human race. It connects the ancient promise of return from exile with the coming of Christ and the worldwide spread of the gospel. As you study, notice how each phrase builds from comfort to universal hope.

Discussion questions

1. What does “the glory of the Lord” mean in your own words? Why is its revelation good news?
2. Isaiah says “all flesh shall see it together.” Who counts as “all flesh” today? How does that challenge or encourage you?
3. The verse ends with “for the mouth of Yahweh has spoken it.” How does God’s speech guarantee the outcome? Where else in Scripture do we see this formula?
4. How do the New Testament writers (Luke 3:4, 6) read this verse? What does that tell us about how prophecy works?
5. In what ways does the church today “prepare the way of the Lord” so others can see his glory?
6. Have you ever experienced a time when God’s glory felt hidden? How does this promise speak to that season?
7. If this promise is certain, how should it change the way we pray for people who do not yet know God?