In this video, Dr. John MacArthur explains how to engage a professing Christian who denies the inerrancy of Scripture.
To a person who says that he is a Christian but denies the inerrancy of Scripture I would say several things. You are denying God’s own claim for the Bible. You are denying what God the Holy Spirit, who authored scripture, says about Scripture—that all Scripture is given by the inspiration of God, that every word is pure, that Scripture is God breathed. Not only that, not only those explicit statements are you denying, but you are denying every time in Scripture it says, “Thus says the Lord.” Then you’re denying the overall superintending power of God over His revelation. Now what that does essentially is to say this: “You are the judge of Scripture.” You’ve just made yourself the authority over the Bible. So, you’re going to be the one we have to trust to tell us what’s true and what’s not true in the Bible. And here’s the problem with that: if you deny inerrancy, the only reason you would ever deny inerrancy would be essentially to deny something in the Bible that you don’t like. And when you’ve done that, you’ve now said what the Bible says about that can’t be true; it’s not true. Once you’ve broken the link in the chain, how do we know that anything is true? So, when the Bible claims inspiration for all of it and you break that then where do you go? How do you trust any of it? You could start, for example, and say, “I don’t believe in Genesis 1–2. I don’t believe in a six-day creation. I believe in some kind of evolutionary process.” That’s not in Genesis 1–2. So the question is, if that’s not true, what else isn’t true? And who’s the person who’s going to tell us what else isn’t true and what isn’t true is hiding something that is true? And where do we go for that? You literally unravel the Scripture if you deny its inerrancy.