This paper using descriptive-analytical method compares theological basis of religious ethics from the perspective of Morteza Mutahhari (Muslim contemporary theologian) and St Benedict (father of western Christian monasticism). Belief in God is the most essential basis for every divine religion and school ofreligious ethics. Islamic and Christian ethics are meaningless without the belief in God. Benedict's moral advices, including major moral virtues namely faith, hope and love, is based on this foundation .Religious sacred texts, which are the sources for valuing moral concepts, shall lose their authenticity, without the belief in God. Belief in God results in the belief in the presence of God at all times and His close observation. This, in turn, will bring about the belief in the Resurrection. Mutahhari, too, considers ethics without the belief in God as invalid and unjustifiable. Sticking to moral principles, which has no worldly benefits, will be reasonable only through the belief in God. He mentions that belief in the Resurrection Day shall be an incentive to adhere to moralities and a guarantee for putting them into practice. Mutahhari and Benedict have almost identical point of view on this subject.