As I noted in a few blog posts, there is a tendency in Christian theology and practice to disregard the Old Testament, or even to actively deny that it has any significance for the Church. Apart from any of the reasons given, such a denial of the Old Testament is probably often because many Christians are ashamed of the Old Testament.
Adolf von Harnack was a well-known German church historian and theologian in the early 20th century. He had Marcionite views and argued that the Old Testament should no longer be normative in the Protestant Church. He writes in his book on Marcion:
The churches are paralzyed, have not been able to create a means through which they could free themselves from the overly old traditions, and also do not find the strength and courage to give honour to the truth; they are afraid of a break with tradition, but do not see or disregard the dire consequences, which result again and again from the continued regard for the Old Testament as holy and therefore inerrant scripture. The greatest number of criticisms, which the populace has against Christianity and the truthfulness of the church, is the consequence of this regard in which the church continues to hold the Old Testament.
In other words: if only the Church discarded the Old Testament, what it would have to say would be easier for society to accept. The Old Testament is inconsistent with the values of a modern society. And it is inconsistent with a Church which modern society would expect.
I want to contrast this with the work of another theologian. In 1947 Karl Barth published the relatively short book Dogmatics in Outline (Dogmatik im Grundriss). In it he also talks about the relationship of Jesus, the Church, Judaism and the Old Testament.
Jesus Christ, in whom we believe, who we Christians as those who are called out of the heathens call saviour, and whom we praise as the one who has brought God’s work for us to completion, he was necessarily a Jew. […] Whoever is ashamed of Israel, is ashamed of Jesus Christ and therefore also of his own existence.
I have permitted myself to contextualize this in relation to the anti-semitic core of National Socialism. It was not an inevitable and trivial matter that in Germany the motto was followed: Judah is the enemy! […] The attack on Judah signifies the attack on the base of the work and revelation of God. Apart from this work and this revelation there is no other. […] Any people that sees itself as chosen and makes itself the basis and measure of all things, such a people has to clash sooner or later with the truly elected people of God. Already in the idea of such a chosen people, even if there is no explicit anti-semitism, there is the essential negation of Israel and through that a negation of Jesus Christ and therefore of God.
In other words, if we are ashamed of Israel and the Old Testament, we deny Christ, we are in conflict with God, we work against God. Christianity stands and falls with the acceptance of the whole Bible. Karl Barth further links such a denial of Judah to an overestimation of one’s own country and culture and then also to such unspeakable acts as committed under National Socialism.
A denial of the Old Testament will not necessarily lead to concentration camps. It will lead, however, to loyalty to other gods apart from the God who is revealed in Jesus. According to the Bible such other gods are idols, which take humans away from the true God. Such idols may well be a country, a movement, an ideology, or a human being, and who knows where they will lead people?
All translations are mine.