This process is called involution, and that which follows is known as evolution, or the unwrapping of the divine essence from the folds of enshrouding matter. The sense of this need of freeing the spirit from that which clogs and binds it is called purity, in whatever part of life it is felt. It is in this sense that we may understand the saying "cleanliness is next to godliness." In the Arabic language the word for purity is Saf, from which root the name Sufi is derived. Some of the early orders of Sufis were called the Brothers or the Knights of Purity; and this did not allude to physical purity but to the unfoldment of the spirit towards its original condition, the pure being of the metaphysician, or the pure reason of the philosopher. The word Sophia or pure wisdom has the same derivation.