Conventionally the word "Sufi" is considered synonymous with the word "mystic". But the word "Sufi", as used in Arabic, Persian, Turkish and Urdu, has a religious connotation. According to the Sufis themselves, the word is derived from an Arabic root "safa" (purity). They opine the sufi is he who keeps his heart pure with God.
The Sufis claim to have inherited their doctrines direct from the teachings of the holy Prophet, who, strictly speaking, has given no dogmatic or mystical theology.
The fundamental of sufism is God, Man and the relation between them, which is Love. The whole sufi theosophy revolves on these three pivots. From God sprang the theory of tawhid (divine unity), of nur (divine light), of zat wa sifat (divine essence and attributes) and the theory of hama ust (all is He). From man emerged the theories of ruh (soul), qurbat (divine proximity), hulul (infusion of divine spirit). From "the relation between God and Man" the Idea of Ishq (divine love), Fana (self-annihilation), Baqa (abiding in God), etc. came into being. Hence the Sufis believe in the real one God who is all merciful and loving and whom a man can approach with a loving heart.