Who held the highest authority in the church during the middle ages and why? the king held the highest authority in the church because he supplied the armies used in wars for the church's crusades. the lord of the manor at each church location held the highest authority because the church depended on income from manor lands. the pope held the highest authority in the church because people believed that the pope was the vessel god used to speak to them. the priest of each church was its highest authority because the priest was educated and had devoted his entire life to the church.