Piper writes an excellent article here. His summary is as follows:
How should Christians respond to this situation? I will suggest ten responses that flow from the Bible.
1. Admit that the Christian church has often been too entangled with civil governments, with the result that violence has been endorsed by the church as a way of accomplishing religious, and not just civil, goals. The Crusades, for example, stand as a monument to collective Christian blindness to the teaching of Jesus. We should make every effort today to avoid political alignments between the Christian church and any civil government or political party. (See my article, Tolerance, Truth-Telling, Violence, and Law.)
2. Make clear that the use of God-sanctioned violence between Israel and the nations in the Old Testament is no longer God’s will for his people. The coming of the Messiah, Jesus Christ, as a suffering servant, rather than a warlord, and his gathering of a people from all nations rather than only one, are two of the many reasons why the Christian church today should not—and almost universally does not—endorse or use violence to promote the gospel of Jesus Christ.
3. Admit that there are many Muslims today who do not approve of violence in the spread of Islam. Admittedly, to many of us in the West, their number seems small and their voice seems muted by the reputation of the more violent strains of Islam. We do not know how large that segment of Islam is.
4. Point out how Islam, in its most sacred writings and authoritative teachings, belittles Jesus Christ, not just occasionally in the news, but constantly by its dominant claims. Islam denies that Jesus Christ was and is God, a central truth of the New Testament and the Christian church (John 1:1-3; Colossians 2:9; Hebrews 1:8). Dominant streams of Islam deny that Jesus died on the cross and therefore deny that the claim that his death atones for sin and propitiates the wrath of God is true (1 Corinthians 15:1-3; Romans 3:21-26; Galatians 3:13; 1 Peter 2:24; 3:18). Therefore, defenders of Islam daily defame Jesus Christ and insult the glory of his gospel.
5. Point out that, in response to this constant defamation of Jesus Christ, there are no public threats or demands for apologies. This is not because we do not love Jesus above all things, or because we have no zeal for the glory of his name. It is because he told us to expect this (Matthew 10:25; John 15:20) and then modeled for us how to react: “When he was reviled, he did not revile in return; when he suffered, he did not threaten, but continued entrusting himself to him who judges justly” (1 Peter 2:23).
6. Do good to those who hate you—and, of course, those of other faiths who don’t hate you (Luke 6:27). This is not because Christians do not believe in vengeance. We simply believe that it is not ours to give. And this age is not the time to give it. This is an age of mercy and patience and forgiveness toward those who malign the King of the universe. He will have his Day of Wrath. But we are too sinful to be entrusted with that righteous judgment. Rather, we should obey the words of the New Testament: “Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, ‘Vengeance is mine, I will repay, says the Lord.’ To the contrary, ‘if your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by so doing you will heap burning coals on his head’” (Romans 12:19-20).
7. Seek to win others to saving faith in Jesus by persuading with words, not imposing with force. This was the way the gospel spread among many religions in the early centuries of the Christian church. The earliest teachers said, “Therefore, knowing the fear of the Lord, we persuade others” (2 Corinthians 5:11). When the New Testament speaks of the “sword of the Spirit” (Ephesians 6:17) or “the weapons of our warfare” (2 Corinthians 10:4), it clearly means the word of God and power of spiritual persuasion.
8. Always be ready to die, but never to kill, for the sake of commending Jesus Christ as the Son of God who died for sinners and rose again as the Lord of the universe. Jesus promises to triumph through our accepting suffering, not our causing suffering. He died to save all who will believe—from every nation and religion. He calls us to follow him on this Calvary Road. “Truly, truly, I say to you, unless a grain of wheat falls into the earth and dies, it remains alone; but if it dies, it bears much fruit” (John 12:24). This is not the death of a suicide-murderer. This is the death of one who loves his enemies and, as he dies, prays, “Father, forgive them, for they know not what they do” (Luke 23:34), and, “Lord, do not hold this sin against them” (Acts 7:60).
9. Pray for the salvation of all those who belittle Jesus Christ. Pray that they would put their faith in Jesus Christ who died for our sins so that if anyone—from any nation or any religion—would embrace him as Lord and Savior and Treasure of their lives, they would be saved from the guilt of sin and the wrath of God. They would have eternal life and joy. This is the way the great apostle Paul prayed: “Brothers, my heart’s desire and prayer to God for them is that they may be saved” (Romans 10:1).
10. No matter the cost, continue to exalt and commend Jesus Christ as the great and only Savior that he is. Say with the apostle Paul, “It is my eager expectation and hope that I will not be at all ashamed, but that with full courage now as always Christ will be honored in my body, whether by life or by death. For to me to live is Christ, and to die is gain.” The day will come when every knee will bow to Jesus as Lord and as God (Philippians 2:10-11). Until that day comes, affirm with Paul: “I do not account my life of any value nor as precious to myself, if only I may finish my course and the ministry that I received from the Lord Jesus, to testify to the gospel of the grace of God” (Acts 20:24).