In my experience, people either follow John MacArthur's every word or disregard him. I have been in the latter camp. It's not that he is a bad guy or that he teaches wrongly, I just find him to be quite belligerent and somewhat condescending. That is the feeling I had while reading this book. I believe that there are very good things that Dr. MacArthur has to say in The Truth War, but it is so very combatant. We do need to stand up and fight for our beliefs, but as Paul says, speak the truth in love (Eph. 4.15).
I wholeheartedly agree with Dr. MacArthur that there is objective truth and that it needs to be declared and adhered to. I do not agree that "nothing in the world is more important or more valuable than the truth." When Dr. MacArthur defines truth for the reader, he says it is "that which is consistent with the mind, will, character, glory, and being of God. Even more to the point: truth is the self-expression of God." I would submit that truth is vitally important, but not the most important thing. Jesus did say that he was the Truth, but in conjunction with the Life and the Way. Not to sound overly spiritual, but if I were to finish the sentence, "nothing in the world is more than important than ____", I would end with "Jesus".
Jesus was Truth, to be sure, but he was so much more. He was Love, Peace, & Holy. Again, I agree with Dr. MacArthur that some today have become to lenient with the Truth of the gospel. However, I also believe that there are many, many things in Scripture that are a foggy mystery & will remain so until we come face to face with Jesus. Dr. MacArthur says that " It [the demise of certainty] is unbelief cloaked in a religious disguise and seeking legitimacy as if it were merely a humbler kind of faith...it is the worst kind of infidelity." Now I would agree - to a point. If you are saying that no truth can be known, that the Scriptures are a guide, a good idea of what the truth is, than yes, that would be classified, to me, as unbelief. However, I hear very few evangelicals saying things like this. What I hear is that people stand by the solid, objective truth of Jesus being the God-Man who actually lived and died for the sins of humanity, bodily arose and will return again for his chosen people. But I would have to believe that the majority of evangelicals are not questioning that, they have questions about the certainty of beliefs such as Calvinism & Arminianism, gifts of the Spirit, and the like. Those things are mysteries & will never be resolved until Jesus comes back. There are mysteries in the Bible - things that we just cannot understand. I am ok with that, I get the sense that Dr. MacArthur is not.
I believe that Dr. MacArthur has good intentions, however, I do not, personally, agree with his approach. For a very good treatment of the postmodern movement and how it effects the church today, I would recommend D.A. Carson's book, Becoming Conversant with the Emerging Church.