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 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 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, defending the faith 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 often stated that we should believe in Him because of the evidence He provided (John 2:23; 10:25; 10:38; 14:29). In fact, the whole Bible is full of divine miracles that confirm what God wants us to believe (Exodus 4:1-8; 1 Kings 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, “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, he is doing apologetics. Some claim that human reason cannot tell us anything about God—but that statement itself is a "reasonable" statement about God. If it’s not, then there is no reason to believe it. 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 (the resurrection) by which Christianity should be accepted or rejected in 1 Corinthians 15? It is only misplaced piety that answers in the negative.
None of this is to say that apologetics alone, apart 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 “Spirit versus Logic.” Why not both? The Holy Spirit must move someone to a position of belief, but how He accomplishes this is up to Him. 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.