Apologetics is the branch of Christian theology that deals with the defense and the establishment of the Christian faith. It often involves answering difficult questions, teaching biblical theology, examining other religions, exposing errors, etc. This can naturally be confrontational, so we are commanded in Scripture to do this with respect and gentleness (1 Pet. 3:15). Evangelism, on the other hand, is the act of presenting the saving gospel (1 Cor. 15:1-4; Rom. 1:16) of Jesus Christ to the lost. It is part of the Great Commission where he told us to "make disciples of every nation" (Matthew 28:18-20).
Nevertheless, apologetics and evangelism are related. When needed, apologetics is a means by which the way is both prepared and protected so that the message of the gospel can properly be presented. Apologetics is like the soldier who battles to protect the messenger who has the gospel to deliver.
When a Christian is evangelizing, and a person in a crowd asks challenging questions, it is appropriate to answer -- unless the person is intending only to be a distraction. Nevertheless, the evangelist should know the basics of apologetics which include knowledge of doctrinal questions, issues of morality, truth, other religions, etc. He or she doesn't need to have exhaustive knowledge, but he should have at least some answers. Apologetics is important -- when needed.
There is a saying, that the heart will not accept what the mind rejects. Though the preaching of the gospel is indeed powerful (Romans 1:16), the truth is that sometimes answering difficult questions and exposing the errors of antagonists can provide a means to more effectively presenting the gospel. The practice of apologetics...
- adds credibility to the speaker.
- helps provide the right to speak the gospel to the crowd. In other words, it helps the listeners better receive what the evangelist is saying because their minds aren't turned away by the speaker's perceived incompetence.
- quiets the objectors.
I have an analogy that I use to demonstrate the relationship between apologetics and evangelism. Consider the world to be a field full of holes, rocks, and crevices with all sorts of obstructions such as thorns, thistles, traps, and false paths. In the center of this field is a garden that is enclosed within a high stone wall that has only a single door. The job of the apologist is to help unbelievers navigate through the dangers and pitfalls of the field in order to bring the person to the Garden's Door so that an encounter with God might occur. Therefore, apologetics can be vitally important by making a way for the gospel message to be preached.
Finally, the role of apologetics is to be subservient to the preaching of the gospel. In other words, it is the practice of preparing the listener to be more able to receive the truth of God's word in the presentation of the saving gospel of Christ. Apologetics is not the power of God to salvation; the gospel is (Rom. 1:16). In fact, apologetics without presenting the gospel has less value, because if you silence a person God may be vindicated and even glorified, but it doesn't mean the person is saved. The gospel is what saves, and apologetics is the servant of the gospel message.