To identify and to recognize the necessary being (God) is among the basic issues of Islamic theology in ‘specific meaning’; such that it has been among most important philosophy objectives and has been regarded as great felicity. Allah as a necessary being is absolute realization and individuality (individuality means being and realization); i.e. his essence is not analyzable even in the mind, because he is the realization of absolute being (existence). There are two major approaches on this issue; in the first one, Fakhr -e- Razi believes that the necessary being has essence and the occurrence of his being on his essence is an external occurrence. In the second one, Mulla Sadra believes that the necessary being doesn’t have any essence in ‘specific meaning’. Though the advocators of both viewpoints have referred to some arguments, the reasons of Razi to affirm the essence of the necessary being and the most reasons of the philosophers to affirm the opposite side are incomplete; hence it is necessary to express the details of these two interpretations of specific meaning of essence.