Today I listened to the next lecture in Professor Philip Daileader's course on the Early Middle Ages. This is what I learned. The decline of literacy in Europe in the 8th century resulted in the Carolingian Empire and the Church moving closer together. The Empire became dependent on clergymen to staff the imperial bureaucracy since clerics were the only class who could to read and write. For its part the Church was dependent on the secular authorities for protection as the times became increasingly perilous.
As the interdependence increased, the church also became an important source of patronage for the Empire. This can be seen in the Constitutio Romana of 824 which was Louis the Pious' way of gaining the veto power over the appointment of the Pope which had been the right of the Byzantine emperor.
Carolingian rules also injected themselves into church councils such as the Council of Frankfurt of 794 which forced the Pope Adrian I to reverse the agreement he had reached with the Byzantines over the issue of iconoclasm.
The Carolingians also actively encouraged Christian missionaries such as St. Wilibrod and St. Boniface (Wynfrith) to convert the Germantic people living to the east. Many of these missionaries where from Anglo-Saxon Britain which had retained strong ties with Saxon communities living in central Europe. St. Boniface famously cut down Donar's Oak, a large tree where pagans worshiped and offered human sacrifices. Converting the Germans was not an easy task and missionaries commissioned The Heliand, which is retelling of the gospel in the form of an epic poem and one of the the earliest works of German literature. Not until the Carolingian's extended their political control to the area did Christianity really take hold.
The Empire was also interested in improving the quality of church personnel. Towards this end they initiated a number of ecclesiastical reforms among the clergy, the bishops, and the monestaries, which had all grown lax. The most enduring reform they introduced was the parish system which is still in use today. To provide a sound financial base the Carolingian introduced a mandatory tithe which was often bitterly resented.
On the monastic front, Louis the Pious supported the efforts of Benedict of Aniane to impose the Rule of Saint Benedict (Benedict of Nursia) on monasteries in their Empire. Like most efforts in the early Middle Ages reforms were spotty and inconsistent.