Religious thought is the form of thought which is concerned with any of the problems of a religious nature within a particular religion, in the same sense that mathematical thought is the form of thought which deals with mathematical questions and solves mathematical problems.
Needless to say religious thought, like other forms of thought, must have reliable sources from which the raw material of its thought originates and upon which it depends. Similarly, the process of reasoning necessary for the solution of mathematical problems must have a series of established mathematical facts and principles.
The single source upon which the divinely revealed religion of Islam depends and upon which it is based, inasmuch as it is based on a revelation of celestial origin, is none other than the Holy Quran. It is the Quran which is the definitive testament of the universal and ever-living prophethood of the Prophet and it is the content of the Quran that bears the substance of the Islamic call. Of course the fact that the Quran is alone the source of Islamic religious thought does not eliminate other sources and origins of correct thinking, as will be explained later.
There are three methods of religious thought in Islam. The Holy Quran in its teachings points to three paths for Muslims to follow in order to comprehend the purposes of religion and the Islamic sciences: (1) the path of the external and formal aspect of religion (the Shari'ah); (2) the path of intellectual understanding; and (3) the path of spiritual comprehension achieved through sincerity (ikhlas) in obeying God.