What’s the difference between knowing and showing Christianity is true? I was first introduced to this helpful distinction by Christian philosopher William Lane Craig. The Bible teaches that a believer knows Christianity is true on the basis of the internal witness of the Holy Spirit. Passages like Rom. 8:16 and Gal. 4:6 make this clear. When we become a follower of Jesus, God’s Spirit then testifies to our spirit that we are His children. In other words, God lets us know directly—without spoken or written words—that we belong to Him, that Jesus Christ has forgiven our sins, and that we have been reconciled to God. This is a kind of rational testimony because the Holy Spirit is a person. And this is how you know that Christianity is true. Showing Christianity to be true involves giving reasons or evidences that are publicly available to everyone. For example, a friend can take you at your word about your assurance that Christianity is true, but he can’t get inside of you to experience it for himself. The task of showing Christianity to be true is ...