What is truth? We began this book with that question, and my earnest hope is that the answer would be clear: Truth is not any individual's opinion or imagination. Truth is what God decrees. And He has given us an infallible source of saving truth in His revealed Word.

For the true Christian, this should not be a complex issue. God's Word is what all pastors and church leaders are commanded to proclaim, in season and out of season—when it is well received and even when it is not (2 Timothy 4:2). It is what every Christian is commanded to read, study, meditate on, and divide rightly. It is what we are called and commissioned by Christ to teach and proclaim to the uttermost parts of the earth.

Is there mystery even in the truth God has revealed? Of course. "'For My thoughts are not your thoughts, nor are your ways My ways,' says the LORD" (Isaiah 55:8). In 1 Corinthians 2:16, Paul paraphrased Isaiah 40:13-14: "Who has known the mind of the LORD that he may instruct Him?"

But then Paul immediately added this: "We have the mind of Christ." Christ has graciously given us enough truth and enough understanding to equip us for every good deed—including the work of earnestly contending for the faith against deceivers who try to twist the truth of the gospel. Although we cannot know the mind of God exhaustively, we certainly can know it sufficiently to be warriors for the cause of truth against the lies of the kingdom of darkness.

And we are commanded to participate in that battle. God Himself sounded the call to battle when His Spirit moved Jude to write his short epistle and it permanently entered the canon of Scripture. This is not a duty any faithful Christian can shirk. Earthly life for the faithful Christian can never be a perpetual state of ease and peace. That's why the New Testament includes so many descriptions of the Christian life as nonstop warfare: Ephesians 6:11-18; 2 Timothy 2:1-4; 2 Timothy 4:7; 2 Corinthians 6:7; 10:3-5; 1 Thessalonians 5:8. Those unwilling to join the fight against untruth and false religion are no true friends of Christ.

The handful of vignettes from church history we have examined together in this book are only a brief introduction to how the Truth War has been fought over the past two millennia. Look at any period of church history and you will discover this significant fact: Whenever the people of God have sought peace with the world or made alliances with false religions, it has meant a period of serious spiritual decline, even to the point where at times the truth seemed almost to be in total eclipse. But whenever Christians have contended earnestly for the faith, the church has grown and the cause of truth has prospered. May it be so in our time.

In other words, the Truth War is a good fight (1 Timothy 6:12). So let's wage good warfare (1 Timothy 1:18)—for the honor of Christ and the glory of God.