Question: "Does the Bible call Christians to defend the faith / argue for the faith?"
Answer: The classic verse promoting apologetics (the defense of the Christian faith) is 1 Peter 3:15, which basically says that believers are to make a defense "for the hope that you have." The only way to do this effectively is to study the reasons for why we believe what we believe. This will prepare us to "demolish arguments and every pretension that sets itself up against the knowledge of God, and take captive every thought to make it obedient to Christ” as Paul said we should (2 Corinthians 10:5). Paul practiced what he preached; in fact, doing apologetics was his regular activity (Philippians 1:7). He refers to apologetics as an aspect of his mission in the same passage (v.16). He also made apologetics a requirement for church leadership in Titus 1:9. Jude, an apostle of Jesus, wrote that "although I was very eager to write to you about the salvation we share, I felt I had to write and urge you to contend for the faith that was once for all entrusted to the saints” (v.3).
Where did the apostles get these ideas? From the Master Himself. Jesus was His own apologetic as He stated time and again that we should believe in Him because of the evidence He provided for what He taught (John 2:23; 10:25; 10:38; 14:29). In fact, the whole Bible is full of miracles specifically being done by God to confirm what He wanted us to believe (Exodus 4:1-8; 1Kings 18:36-39; Acts 2:22-43; Hebrews 2:3-4; 2 Corinthians 12:12). People rightly refuse to believe something without evidence. Since God created humans as rational beings, we should not be surprised when He expects us to live rationally. As Norman Geisler says, “This does not mean there is no room for faith. But God wants us to take a step of faith in the light of evidence, rather than to leap in the dark.”
Those who oppose these clear biblical teachings and examples may say things like, “The Word of God does not need to be defended!” But which of the world’s writings are the word of God? As soon as someone answers that, they are doing apologetics. (How well they do it might be another story!) Some claim that human reason cannot tell us anything about God—but isn’t that a "reasonable" statement about God? If not, then there is no reason to believe it, and if so, then they have contradicted themselves. A favorite saying is, “If someone can talk you into Christianity then someone else can talk you out.” Why is this a problem? Did not Paul himself give a criterion by which Christianity should be accepted or rejected in 1 Corinthians 15? It is only misplaced piety that answers in the negative.
Now none of this is to say that bare apologetics, free from the influence of the Holy Spirit, can bring someone to saving faith. This creates a false dilemma in the minds of many. But it does not have to be “Sprit vs. Logic.” Why not both? We must not confuse the fact that the Holy Spirit is required to move one into a position of belief with how He accomplishes this feat. With some people God uses trials, in others it is an emotional experience, in others it is through reason. God can use whatever means He wants. We, however, are commanded to use apologetics in as many or more places as we are told to preach the gospel. How is it then that all churches affirm the latter but so many ignore the former?