Two paragraph sample but do read the whole piece:
Medieval Europe was inhabited by a collection of tribes and states, shot through with tendrils of Christianity following the remains of the Roman Empire and with the Islamic world pushing up in Spain. European culture, considered as a specific constellation of ideas, modes of expression, and forms of organization, hardly existed, nor did any of those people think of themselves are European. Europe, as such, originated in Christendom, and the core institution of Christendom, the Christian Church, was held together, not only by religious doctrine, but by religious ritual and practice.
Plainsong was at the center of that ritual, and much religious practice as well. During the medieval period most plainsong was used within religious communities as a daily aspect of their religious life, rather than being performed with a congregation on Sundays. While this body of music has its roots in pre-Christian music of the Jewish service, it is generally known as Gregorian chant, after Pope Gregory I, who played a major role in organizing and codifying the chants late in the 6th Century CE. these chants are generally regarded as the fountainhead of Western classical music, all of whose forms have some link to this Gregorian lineage, though many other musics will eventually be put to classical use. For this reason we can think of the classical music as developing under a Gregorian Contract.