If you are asking questions like these, then you must read K. Scott Oliphint's The Battle Belongs to the Lord. It is a simple introductory work which turns to Scripture to understand God's call for his people to defend the faith.
After applying insights from the biblical battle between David and Goliath in 1 Samuel 17, Oliphint structures his book around explaining what several key biblical passages reveal to us about our apologetic work. The chapters include examinations of 1 Peter 3:15-17; Jude 1:3; 2 Corinthians 10:3-5; Romans 1:16-18, 19-32; and Acts 17:15-34.
Oliphint summarizes his central concern by saying:
Since Christ is Lord, and the battle is his, we must always be ready to contend for the faith once for all delivered to the saints. We must use the weapons, not of this world, but of the Lord. We must take every thought captive to the obedience of Christ as we demolish the arguments, with gentleness and reverence, of those who suppress the truth in unrighteousness, exchanging the truth of God for a lie, worshipping created things, rather than the Creator, who is blessed forever. Amen.
What an excellent statement! And every phrase of it comes from God's Word. Why should we begin with anything other than God's own revelation in learning more about defending the faith?
I simply cannot recommend this book highly enough. It is filled with biblical insight. Additionally, Oliphint includes study and application questions at the end of each chapter, making it a great teaching tool or small group study. I am simply amazed that he has managed to compress so much in less than 200 pages.
At the same time, this work should be seen as the beginning of fruitful apologetic study. It is an introduction to the Christian life of gospel proclamation and defense. More detail and depth will come through reading other material. Nevertheless, Oliphint has provided us with an invaluable starting point. Every follower of Christ will find this book spiritually challenging and edifying.