The new religious paradigm that appears in the 7th century is the source of a lot of change in the Middle East. Islam and its great and rapid expansion offer a new way of political, social, cultural, linguistical life.The shift from the different languages as Greek, Syriac and others to Arabic marks the opening of new cultural exchanges and specially in the theological milieu. Indeed, Christians in the area are soon changing their liturgy into Arabic and also to write about their faith in Arabic. The first Christian theological writing in Arabic is found in a manuscript from the 8th century from mount Sinaï. The text is aiming an apologetical goal while being written in an Islamic way. The core of the presentation of the unkown author is to defend the Christian faith at this time where Islam is gaining power and space throughout the world. The two main topics developed are the identity of God and the unity in the Trinity and the identity of Jesus and Christology. The methodology used by the author is simple: he develops analogy and scriptural proof to demonstrate the accuracy of Christian theology. The response to these first steps into Christian theology in Arabic is interesting specially in the opus of al-Qāsim al-Rassī in his radd ‘alā al-Naṣārā. He uses the same methodology the author used in the treaty of Christian theology: he uses analogy and the quotation of scriptures either biblical or from the Quran and then shifts to negative theology and opening a door after him to a new relationship between Muslim scholars and Christian scriptures. The goal of this presentation is to present this new method to do theology, presenting it as an Arabic kalām, and then focus on the opus of al-Qāsim al-Rassī and see how this Arabic kalām with the help of the Bible and reason is a source of hermeneutic of some Quranic passages.