Putting aside many themes on Marcion worth studying, this thesis concentrates on his interpreting the OT. Apart from the main stream of the interpretation in his age, he reads OT literally. Relying on this method he can insist, that the God in OT acting cruel, enjoying war and blood, and laying burden like laws on human being is evil(Isa. 45: 7) and so different from the good God by Jesus. This later one has been unknown until the advent of Jesus. He plans to regain the intact Evangelium of the highest god through discarding OT and cleaning the contaminated scriptures he sees as Evangelium, i. e. Gospel of Luke and 10 pauline letters. His theological effort interpreted from his understanding OT is nothing but an establishing the Identity of Christianity. Christianity is for him perfect new, unknown and so unrelated to Judaism. Opposing to the big church accepting the OT as the sola canon, namely one testament, he makes it as the document truly showing the world being evil and it’s cause. His theological effort could have given, as Campenhausen said, the shock to the big church to try to harmonize two testaments. In oder not to say, that both testaments repeat the same truth, the church should find out some picture describing the whole history of the world: Heilsgeschichte. Apart from the evaluating him dogmatically it should be admitted, that in controversy with his theology the Christianity became the Religion, which has the canon consisting of two testaments and at the same time the historical perspective from the beginning of the world to the end of all.