In the words of 1 Peter 3:15, the personal prerequisite for offering a reasoned defense of the Christian faith is to have “set apart Christ as Lord in your hearts.” Christ must be the ultimate authority over our philosophy, our reasoning, and our argumentation–not just at the end, but at the beginning, of the apologetical endeavor. If we are to “cast down reasonings and every high thing exalted against the knowledge of God,” said Paul, then we must “bring every thought captive to the obedience of Christ” (2 Cor. 10:5). An ultimate commitment to Christ covers the entire range of human activity, including every aspect of intellectual endeavor. To reason in a way that does not recognize this is to transgress the first and great commandment: “You shall love the Lord your God with … all your mind” (Mt. 22:37). In light of this, our apologetical method, not merely our apologetical conclusions, should be controlled by the word of God.”
Greg Bahnsen, Van Til’s Apologetic (P&R, 1998), p2.