Christians and the Qur'an
One stipulation which I don't believe Levy-Rubin dealt with, however, is "We shall neither learn the Qur'an nor teach it to our children." (EBL is down for maintenance, so I can't check for sure.) This clause was, however, the focus of a chapter in the outstanding edited volume The Place to Go: Contexts of Learning in Baghdad 750-1000 C.E. The stipulation mentioned seems peculiar for a missionary religion and has often been taken as simply another way of marking boundaries between the ruling class and others. In this chapter, however, Clare Wilde argues instead that it arose from a concern with properly reverential approaches to Islam's sacred text, as well as the fact Christians often used the Qur'an to argue on behalf of their own religion.
The latter, of course, involved accepted the Qur'an as a divinely revealed text, but highlighting ways in which it could be read and confirming Christianity. Christian exposure to the Qur'an owed something to its use as a tool in learning Arabic, which by the ninth century had become the lingua franca of the imperial elite. Much as Muslims found support of Islam in the Bible, Christians looked at Qur'an 4:171, which refers to Jesus as the word and spirit of God, as indicating his divine status, especially in the context of the Muslim theological disputes over the nature of the Qur'an as God's word. The mysterious letters which begin some suras were also interpreted as supporting Christianity. Sura two, which begins a-l-m, was seen as referring to the Messiah, "al-masih."
Wilde also highlights a few other aspects of the Covenant of Umar's prohibition, such as whether banning non-Muslims from a key Arabic instructional text could have been designed to hinder their fluency in the educated form of the language. The point here is, though, that it is a complex document which arose in a certain time and place under certain social and cultural conditions, and we have to understand those conditions to understand the document and its intentions.