Concepts and Symbols by Charles Upton
The central doctrine of Islam is al-tawhid, Unity. God is One; there is no god but God. And the Unity of God is reflected in the universe, in the unity of nature's laws, as well as in the uniqueness of each object in nature. To construct circles is to make a geometrical diagram of al-tawhid.
The Arabic word for 'heart', qalb, is derived from the root QLB or QBL, which embraces a number of concepts having to do with 'turning'. In Sufi metaphysics the Heart is the centre of the psyche, the point at which it is intersected by the vertical ray of the Spirit (ruh). This symbolic image has obvious affinities with the act of constructing a circle using a compass and a sheet of paper. The Heart is who we really are in the sight of God; it is the central point of our full and authentic humanity. Whoever wants to rise along the vertical path of the Spirit, the axis mundi, first has to have reached the Centre, the Heart, which is another way of saying that we can't relate to God with only a part of ourselves. A line drawn from any point on the circumference of a circle so as to intersect a line passing vertically through the circle's centre can never be one with the infinite elevation which the vertical line symbolises.