I am trying here to prevent anyone saying the really foolish thing that people often say about Him: "I'm ready to accept Jesus as a great moral teacher, but I don't accept His claim to be God." That is the one thing we must not say. A man who was merely a man and said the sort of things Jesus said would not be a great moral teacher. He would either be a lunatic--on the level with the man who says he is a poached egg--or else he would be the Devil of Hell. You must make your choice. Either this man was, and is, the Son of God: or else a madman or something worse. You can shut Him up for a fool, you can spit at Him and kill Him as a demon; or you can fall at His feet and call Him Lord and God. But let us not come with any patronizing nonsense about His being a great human teacher. He has not left that open to us. He did not intend to. (Mere Christianity, ch. 3: "The Shocking Alternative", p. 40-41 [in my version])This statement concludes a section in which Lewis has been dealing with the record of revelation of the two Testaments. The Old Testament has revealed to the Jews what God is like, who he is, what he demands of his creatures. Then the New Testament opens up with Jesus, "a man who goes around talking as if He was God" (40).
I was reading Hans Urs von Balthasar's Explorations in Theology: I: The Word Made Flesh, the other day, when I came across a very similar statement to Lewis's above. Like Lewis, Balthasar is talking about the revelation of God in the Old Testament and how Christ manifests his unique status as God incarnate in the New Testament, displayed in his words and deeds. Then, Balthasar concludes this section with this:
The argument from Christ as manifested in scripture has, all through history, both ecclesiastical and secular, refuted with a truly divine irony all the insidious suggestions of his enemies. It is so cogent because the recorded facts rule out the alternative: either Son of God or else purely man of the highest religious perceptions. It compels this other alternative (as philology and psychology might propose): either Son of God or else the hallucinatory invention of enthusiastic followers, God's Son or psychopath. Anyone who thinks "religious genius" is a sufficient explanation has certainly not read the New Testament objectively. All attempts to bring the unique figure of Christ within general laws miscarry; they fall back for an explanation on deception or mental disorder, as the Jews did once and have always done (Mt. 28:15; Jn. 8:48). (p. 56)They have their own unique voice of course and likely different audiences in mind. Lewis first communicated what later became Mere Christianity as BBC radio talks to England during WWII (perhaps 1943 or so). Balthasar's was first published in German in 1960, translated to English in 1964. Had Balthasar read Lewis? I've seen him refer to Lewis in other works. There is no note here.
However, I think anyone might come to the same conclusions these authors did merely by reading the gospel accounts of Jesus' life and words in light of the Old Testament. The Old Testament teaches that forgiveness of sin requires confession and restitution with the individual wronged, as well as sacrifice and repentance before God. And yet here Jesus goes around forgiving people's sins, none of which were directed toward him personally, as a man in Palestine, but toward others and primarily toward God. So on what authority is Jesus forgiving sins? - the very question the Pharisees and scribes asked him. A good moral teacher doesn't presume to forgive the sins one person commits against a third party, nor would they presume to speak for God. A good moral teacher does not presume to know the mind of the wronged party, not present and involved in the conversation, nor would they presume to know God's mind on the matter, for only God can read the thoughts and attitudes of hearts. Only God can forgive sin, as the Pharisees recognize. No wonder they tore their clothes and picked up stones to stone him. Jesus' enemies in his day recognized full well that he was claiming to be far more than a good moral teacher or an enlightened religious guru. He was claiming to be God and they knew it because they paid attention to what he was saying, which is something that anyone who chalks Jesus up as merely a good man is not doing. Jesus could only forgive sins because he was God and because he himself was going to atone for them for all who put their faith in him.