Titus Burckhardt describes the mihrāb as ‘indisputably a creation of sacred art’, an area in every masjid which indicates the qibla, or direction of the Kāba in Makkah. Art historians believe this element was introduced into masjid architecture during the Umayyad caliph al-Walīd, it’s probable the design replaced a simplified door form, indicating the direction of Makkah.
‘It’s very shape, with its vault corresponding to heaven and it’s piedroit to the earth, makes the niche a consistent image of the “cave of the world”. The cave of the world is the “place of appearance” (mazhar) of the Divinity, whether it be the case of the outward world as a whole or the inner world, the sacred cave of the heart’.
‘To establish the symbolism of the mihrāb in its Islamic perspective, it must be related to its Koranic context. the word means, literally, “refuge”.’
‘It may seem surprising that a form such as the mihrāb which is, after all, simply an accessory to the liturgy, should be the focus of a particularly rich symbolism. But this is implicit proof of the link between sacred art and esotericism, the “science of the inward” (‘ilm al-bātin).’
Source; Titus Burckhardt ‘Art of Islam, Language and Meaning’ (2009, p.90-95)