R.C. Sproul in his book, Defending Your Faith: An Introduction to Apologetics, said that the apologist’s task is to provide proof and to be persuasive. He goes on to say:
Proof is objective and persuasion is subjective. People who are hostile to certain ideas may have those ideas proven to them, but in their bias they refuse to be persuaded – even by the soundest of arguments.
Apologetics, for this reason, is not merely about winning an argument. It is about winning souls. The old aphorism rings true: “People convinced against their will hold the same opinions still.” That is why, for example, if a Christian were to “win” an intellectual debate with a non-Christian, the victory celebration may never take place. The non-Christian might concede defeat, though usually not until his head hits his pillow at the end of the day. This may never translate into conversion, but there is some value to this aspect of “winning” an argument. On the one hand, as Calvin said, the unbridled barking of the ungodly may be restrained; and on the other, the intellectual victory provides assurance and protection to the young Christian who is not yet able to repel the bombardment of criticism from scholars and skeptics. It serves as a confirmation of the Christian’s faith.
The Christian bothers to engage in apologetics because, quite simply, how will the nonbeliever hear the truth of Christ Jesus “without someone preaching?” (Romans 10:14 c), (pg. 18).