In Islamic architecture, the octagon is a Qur’anic symbol of Paradise. There is no end of spiritual insight once that symbol serves as a support to begin contemplation.
If you are looking for a symbol of Islam as a whole, that would be the Ka‘bah. The whole reality and doctrine of Islam are summed up in its shape, its unity, and its centrality.
The Ka‘bah is a meta-cosmic symbol. It has six faces showing the six directions in three dimensions, but all the directions are completely drawn into the Center. Its compactness is thus a symbol of tawhîd. The three dimensions recall the three planes on the spiritual path: the Will, the Soul, and the Intellect; sharî‘ah (law), tarîqah (path), and haqîqah (Reality) — each with a dual aspect, active and passive, or objective and subjective.
It is a crystalline shape, recalling the symbolism of crystals, which although they are stones, transmit light. Just as the religion of Islam takes place in this world, but retains the pristine purity of the Transcendent.
The centrality of the Ka‘bah, with all the worshipers facing inward toward the center, is again a tangible symbol of tawhîd. The circumference of the circle is the sharî‘ah, the radius into the center the tarîqah, and the center itself is the haqîqah.
Come you lost atoms to your Center draw,
And be the eternal mirror that you saw:
Rays that have wander'd into Darkness wide
Return, and back into your Sun subside.
Written by Owais Jafery