Question: "What does it mean and when will it happen that every knee shall bow?"
Answer: The phrase “every knee shall bow” comes from the Old Testament book of Isaiah. In the last half of the book (chapters 40—66), God prophesies through Isaiah the coming comfort to His people, Israel, who are in exile in Babylon for their covenant unfaithfulness. The phrase in question is found in Isaiah 45:23, which reads, “By myself I have sworn; from my mouth has gone out in righteousness a word that shall not return: To me every knee shall bow, every tongue shall swear allegiance.”
The main thrust of the overall passage is that God is the only one who can save His people, as opposed to the idols that are worshiped by the nations. God is God and there is no other (Isaiah 45:5–6, 18, 22). Those who turn from their idols will be saved. Those who do not will be ashamed. The bottom line is that, before God, every knee shall bow and every tongue swear allegiance to God.
The apostle Paul quotes this passage twice in his writings, once in Romans 14:11 and again in Philippians 2:10–11. In the Romans context, Paul is writing about Christian liberty. The Christian is not to pass judgment on his brother or sister in Christ over non-essential issues—the examples given in the text are dietary habits and religious days of observance. In these things to which the Lord gave no specific command, we should not stand in judgment of our brothers or sisters in Christ.
The other quote, Philippians 2:10–11, comes in that wonderful Christological passage, the overall context of which is the call to Christian humility and how we should not consider ourselves better than others. Rather, we should look out for the interests of others above our own. In vv. 5–11, Paul uses Christ as the ultimate example of humility that we should follow. It was Christ who, being in the very form of God, emptied Himself and took on the form of a servant. In doing so, He became obedient to God to the point of death. This He did for the sake of His people. It is important to note the overarching theme of this passage—the humiliation and exaltation of Christ. Christ first humbles Himself and then submits Himself in complete obedience to the Father. Afterwards, the Father highly exalts Him above all things. Paul cites Isaiah 45:23 to say that at the feet of Jesus every knee will bow and every tongue confess that Jesus is the Lord to the glory of God the Father.
In both of Paul’s citations of Isaiah 45:23, he is echoing the truth that there will come a time when “every knee shall bow and every tongue confess” to the glory of God. In the Philippians citation, Paul is declaring the divinity of Jesus when he says that every knee will bow and every tongue will confess Him as Lord. This is a clear indication of what will occur at the Second Coming of Christ. During the first advent, Christ came in humiliation and died a humiliating death on the cross for the sins of the world. In His second advent, Christ will come with power as the Conquering King. When that happens, it will be as our Lord Himself predicted in the Olivet Discourse (Matthew 25:31–46) and as the vision the apostle John received in Revelation 20:11–15. When the King of kings and the Lord of lords returns to this earth, then will come true what the prophet Isaiah foretold all those years ago: “Every knee shall bow and every tongue shall swear allegiance.”
The lesson for those living in the “here and now” is that we must heed the warning of the writer of Hebrews who said: “So, as the Holy Spirit says: ‘Today, if you hear his voice, do not harden your hearts as you did in the rebellion, during the time of testing in the desert, where your fathers tested and tried me and for forty years saw what I did. That is why I was angry with that generation, and I said, “Their hearts are always going astray, and they have not known my ways.” So I declared on oath in my anger, “They shall never enter my rest”’” (Hebrews 3:7–11, citing Psalm 95:7–11).
If we have heard and responded to the gospel, then we must live each day in light of its truth, shining the light of Christ into a dark world. Those who have not responded to the gospel are exhorted to respond today and not harden the heart. It is appointed for each of us to die once and then to face the judgment (Hebrews 9:27). Every knee will bow and every tongue will confess that Jesus Christ is Lord to the glory of God the Father. Those who have responded to the gospel with faith and repentance will do so gladly and willingly. Those who have hardened their hearts to the call of the gospel will do so with great fear and trembling.