Within the discipline of Christian apologetics, there are several sub-disciplines, philosophy being among them. Apologetics can be done in an “offensive” way (where arguments are presented for Christianity’s truth) and in a “defensive” way (where a defense of Christianity is made against anti-Christian arguments and objections). However, another method I am interested in serves as an apologetic to believers (rather than simply unbelievers). The point in these cases is not to convert as much as it is to strengthen. This could be called “edification apologetics.”
In general, this could involve either positive arguments for God or defenses of the coherence of Christianity or whatever it might be. There is a definite distinction in the way edification apologetics is utilized compared to the traditional method. In discourse with atheists or other non-believers, I will find that the objector claims (or acts in such a way as to claim) he will not believe unless rationally compelled to do so. This is quite the tall order for almost any argument. Instead, the goal of edification apologetics is not to believe only what one is rationally compelled to believe, but rather to embrace what one is justified in embracing.
Justification for believing some proposition or truth is not an easy thing. Volumes have been written about epistemology and I will not go too far with this here. However, it certainly is not the case that justification necessarily involves certainty, or necessitates one is rationally compelled to believe the truth that he does believe. In fact, it’s entirely plausible that one is justified in believing some proposition that turns out to be false.
I have found that if someone insists he will not believe unless compelled to do so, then he simply will not have the kind of belief needed to justify faith. Certainly, faith is not blind and has its reasons, but it’s difficult to see a scenario in which one is rationally compelled to believe the Gospel and faith is involved. Instead, I find it far more productive to show believers they are rationally justified in the faith. What good does this do?
First, a strengthened believer can go on with his Christian life. Many believers, when stuck in a season of doubt, are frozen in their spiritual walk. Perhaps it is the case they keep on performing their activities and duties, but on the inside they are non-functional. Second, a strengthened believer will be dissuaded from a season of apostasy. I talk to believers all the time who are desperate for answers to questions that torment them, only to hear their questions have been dismissed or just to “have faith.” If these believers do not get answers, 90% of the time they will eventually fall away (arbitrary number used for effect). Third, a strengthened believer will be a better part of the body of Christ (Eph. 4). The Christian who understands more about God and logic is better prepared to serve the body of believers than he was when he was in doubt. Finally, a strengthened believer will be better equipped to do evangelistic apologetics to the non-believers (and unbelievers) of the world.
An example of edification apologetics, or showing the believer he is justified in his belief, could be the moral argument. "If objective moral values do exist, then the best explanation of their existence is God. Objective moral values do exist. Therefore, their best explanation is God." One may claim he is not rationally compelled to accept either of the two premises, but one is certainly justified in doing so (who would think, for example, that claiming moral values exist is utterly bereft of justification? Skepticism I can understand; outright denial of the obvious seems less so).
I have no doubt that edification apologetics is necessary for Christians to be able to be successful in evangelistic apologetics. We must prepare believers to give an answer for the hope that lies in them, and the hope of the world, Jesus Christ.
 Of course, when the subject realizes the proposition is false (or comes to know the evidence or facts that should rationally lead someone to the knowledge of its falsehood), he is no longer justified in believing it.