Sufism elaborates on the relationship between God and humans as it is found in mainstream Islam, and so it is initially derived from interpretations of the Quran and the hadith. Alongside those two texts, which all Muslims use as the bases for their spiritual, legal, and social systems, Sufi wisdom literature, in the form of sayings and biographies of Sufi masters and sages, articulates a vision and practice for the achievement of enlightenment through ultimate union with the Divine.
Thus in addition to the acceptance of mainstream Muslim narratives and points of dogma concerning the five pillars of Islam (prayer, charity, pilgrimage, testification that there is one God and that Muhammad is his Messenger, and fasting during the month of Ramadan), Sufism imparts an additional dimension to the life of the practitioner of mysticism. Many Sufi texts describe the path to spiritual perfection as a matter of passing from the realm of the Unreal to the Real, that is, from one's actual existence to one's intended spiritual perfection.
According to modern scholar William Chittick, Sufi beliefs about the difference between what is Unreal and what is Real stem from an interpretation of the standard Muslim testification of faith, the Shahada. In the statement "There is no god but God," there is a judgment about something that is and something that is not—about an unreality and a reality. From this, according to the logic of this argument, God exists in a manner that is unique and totally exclusive. Sufis came to define that unique type of existence as Absolute Reality. The quality of existing in an Absolute, namely unique and solitary way, belongs only to the One God. Since God alone has Absolute Reality, everything else in the universe belongs to the realm of the Unreal, the non-absolute, or relative world.
One of the most oft-cited texts for this theory of God's Absolute and therefore unique manner of existing is the Quranic verse "Everything is perishing except His (God's) face" (Quran 28:88). This verse is taken as proof that the world as we know it is not eternal, not absolute, and therefore not ultimately Real. The only thing that is Real is God (here embodied by the phrase "God's face") and therefore He is the only Reality that will endure when all Unreality has passed away. This theoretical dualism, oscillating between the Real and the Unreal, is also reflected in the poetry of the mystic and poet Rumi, who wrote "God turns you from one feeling to another and teaches by means of opposites, so that you will have two wings to fly, not one."
Also based on the language of the Quran is the belief that what the world can provide for believers are signs. The verses of the Quran are referred to, in the text itself, as ayat, which means signs. Therefore, even though the world is only relatively real, within it the believer can seek to discern differences among the various phenomena in the world, any of which may be a sign, ayah, sent by God. Different phenomena reflect different aspects and levels of God's communication with human beings. Thus a prophet, for example, reflects and conveys divine reality more significantly than the average person. The principle of discerning which signs are significant is therefore part of what practitioners of this mystical expression of Islam call "walking the Sufi path."
Similarly, the second half of the Shahada, "Muhammad is the Messenger of God," reflects the value of beings in the world while ultimately acknowledging that only God is Absolute. In singling out Muhammad and staking a claim in belief in his status as a Messenger, one acknowledges that God uses people in the world to reflect and communicate about Himself. The revelation communicated by Muhammad is therefore coming from God, and is a manifestation of God's uniquely Real Being. Once the Sufi, applying this mystical interpretation of the Shahada, initially discerns between the Unreal and the Real, she/he can then discern between the human and Divine aspects of all objects and people in the world.
Through rigorous practice and perfection of the soul (called tazkiyat al-nafs), the Sufi practitioner seeks to achieve a proper understanding of the universe, at which point she/he will discern the only Ultimate Reality, God. These practices include invocations, prayers, and communal gatherings, and may also include superogatory (i.e., beyond the month of Ramadan) fasting. By becoming inured to the bodily or merely physical demands of earthly existence, this training aids the Sufi in banishing a preoccupation with the material self, the nafs, after which it will cease to exist and in this way, allow the Sufi to turn solely to God.
It is important to stress that the broader cosmological framework within which Sufism operates is not different from general Islam. This is because Sufism is not a denomination or a sectarian affiliation, such as Sunnism or Shiism. Rather, Sufism is the mystical expression of the Islamic ethos, which is not strictly Sunni or Shii. Thus, Sufis also believe, like all Muslims do, that God created the world, that he sent messengers and prophets such as Abraham, Moses, Jesus, and Muhammad with messages and scriptures to guide humankind. All of this is consistent with mainstream Muslim belief.
Sufis do not so much differ from as add to that tradition, accompanying what is seen as traditionally orthodox practice with an additional layer of personal and inwardly-directed spiritual attention. The purpose of this additional dimension is to develop a personal relationship with God that happens to follow specifically Sufi principles of renunciation and spiritual training. As stated above, however, Sufism is not exclusive or generally prescriptive: that is, every Sufi is a Muslim, but not every Muslim must be a Sufi.