Answer:
The 'Song of Roland' is a poem, which reflects the Battle of Roncevaux Pass, during the reign of Charlemagne in France.
The connection between the King and Vassals is prominent because it seems to be the one joining features between the Christians and Muslims and there is the understanding that without this trust on a system of authority, medieval society would break.
Considering the Muslims were not faithful to their god, they had no reason and right to have the god's rewards since they have no devotion toward God and are considered to the evil by the Christians. The support of God is thus seen to be falling upon the Christians and the close contact between Charlemagne and God can be seen in decisions made by this king and his army.