"For we must all appear before the judgment seat of Christ; that every one may receive the things done in his body, according to that he hath done, whether it be good or bad. Knowing therefore the terror of the Lord, we persuade men;" (2 Cor. 5:10-11a)
In our apologetic endeavors in conversation with unbelievers, we both defend the faith and proclaim the truth of God to lost souls. The true situation is that we are both creatures of God and that the unbeliever is in need of a Savior. The conversation is meaningful, rational and intelligible.
To the atheist unbeliever, we are all matter-in-motion, assembled by chance, a mere piece of the universe, yet (somehow) free from the universe -- in need of nothing. In this case, the conversation would be meaningless and unintelligible.
Our apologetic is built on the fact that we are both creatures of God, and we should not compromise this truth by way of a method that lends credence to the unbeliever's pretension to the contrary. On the atheist's view, the fact of a rational conversation itself is inexplicable.