There is a big difference between the function of Christian art and Islamic art... which caused a difference in the general appearance between them even though they both grew up in almost the same place..
One of the defining characteristic of the ancient jewish tradition, a characteristic which other dominant middle east tradition did not have , was the iconoclasm. the interdiction of representation of living being, especially human representation in fear that the veneration towards God could be wrongly mis-directed. The old byzantin christian tradition had many iconoclastic debates and in some periods the icons of saints decorating churches were destroyed. But in old both eastern and western christianity in the middle age, Jesus and the life of saints have been represented in churches which one of the major difference with jewish temples and Islamic musk during the same period which conformed to strict iconoclasm. Since human are attracked by beauty and the powerfull and rich need to impress by building gigantic places of cult with beautifull architecture and nice decoration. The decorative technique which consist in all kind of symmetric geometric patterns are pleasing the eyes while being totally iconoclastic in representin nothing reminiscent of the living. Islamic art has been characterized by this extensive geometrical style. The high middle age has seen the construction of the gothic cathedral which is very geometrical in itself. Here the gravitational forces are being transmitted to the ground in a way that is optimal and explicit in the architecture allowing gigantic opening covert with glasses in geometrical patterns. The elements of representation of saints in these cathedral are impressive and important but not as impressive as the geometrical structure of these building and their opening. Renaissance will change this balance and goes much further towards a realistic style of representation which to my taste is not as beautifull as the middle age gothic cathedrals.
Interesting debate but chronology needs to be explored in a little more detail. Generally most historians speak of the Middle Ages as beginning c500CE. By then Christianity has been around over 400 years and there was already a growing difference between that east and west. The prophet Mohammed was born c570CE. It may be worth defining a period of the Middle Ages (ends around 1400CE) where the comparison is being made. Certainly for both Abrahamic faiths there was much change both in function and style over the millennium of the period
It was a very useful dialogue.. Your opinion is very important, especially with regard to Islam's position on icons and the prohibition of representing the human being. Here is a point of fundamental disagreement between Islamic art and Christian art.
But was the iconoclasm movement in the Eastern Church one of the influences of Islamic thought?
You perhaps need to look at the Iconoclastic Controversy in the eastern church (8-9th century CE) and the response in the western church. It proved to be a major issue about the function of art (icons) in Christian worship.
A good short introduction to some of the issues can be found in
Inventing Byzantine Iconaclasm (Studies in Early Medieval History) by Leslie Brubaker punished by Bristol classical Press in 2012
Leslie Brubaker is an expert in Byzantine illustrated manuscripts and was appointed the Professor of Byzantine Art at the University of Birmingham in 2005.
With the fall of Rome in 476 CE, literacy took a major hit. By 800CE Charlemagne reinstituted the Carolingian Revival to get priests to read. The use of icons and pictures became a means by which the Western church taught illiterate people the stories of the Bible. The human forms were forbidden among the Jews as being either idolatry or taking attention away from Yahweh, who was a spirit. Initially, the images of the Holy Family were denoted with a halo that later became icons of veneration. Could the initial function have been something as simple as teaching illiterate people basic religious truths and developed from there?
Your interpretation of the emergence of Christian icons is interesting .. and it may apply to the region of Europe after the fall of Rome ... but the appearance of icons dates back to about 3 centuries before the fall of Rome, and at that time literacy was common in Christian societies, and the use of icons continued after the fall of Rome in countries that were scientifically advanced Its peoples know how to read and write, such as Byzantium, Syria, Palestine and Egypt, so the appearance of icons cannot be explained as being a means of knowledge, but that icons were a means of religion.
Christian art is didactic and usually naturalistic and figural, because of the emphasis in Christian theology on the body of Christ. Islam, meanwhile, focuses on the word of God and its art relies mainly on abstract patterns.
The objectives were different: while Christianity "praised" the key figures of its religion (Christ and the Saints), Islam, preventing the depiction of divinity, used geometry to depict the infinite intersections of life, as well as the wonders of "creation".
Both Islamic and Christian art spans over decades and takes on a wide range of forms and genres.however, Islamic art tend to abide by the concept of aniconism; that is, the belief that the creation of living beings, like humans, is a job for God and should therefore be left out of artwork. This also partly prohibits idolatry, or worshiping an image in place of God.while the Christian art deals specially with human objects and forms which brings religious forms and images to life which depicts or shows different beliefs through illustrations from the life of Jesus.
Well done... This is exactly the difference between Islamic art and Christian art..
It was the position of Muslim religious scholars regarding the depiction of humans and animals that determined the form of Islamic art, which tended to depict plants, and then Muslims excelled in that art.