As Astraea, Garl Vinland, Selen Vinland, and Father Vinland (an important cleric) all hail from the Western Highlands (an area not visited by the player) it is believed to be the base of operations of the Church of Boletaria. The highest level of clerics (such as Father Vinland and Saint Urbain) serve as spiritual leaders, speak to God, pray for the safety of the holy warriors, and perform great miracles; they do not take up arms in conflict.
The next level down are the high-ranked knights, commanding officers of the Church. They likely devise a plan of attack and lead priests and temple knights into battle. Selen Vinland definitely fits into this category as she wears dull gold armor which signifies high rank. Saint Urbain refers to Vito the Moonlight knight and Risaia of Istarel as having similar rank as Selen Vinland so they would also fit into this category. High rank comes with it the privilege of wearing armor which grants great protection and wielding powerful, ancient weapons which are often holy relics.
The next level down are the priests and temple knights who are the foot soldiers of the Church. Priests are believers of the word of God, spread its message, and serve as regular infantry. As they are more introspective, they have a better grasp on performing miracles than temple knights. Priests wear chain mail armor, carry a heater shield, talisman of God, and use simple blunt weapons such as the mace, morning star, or the war pick. Temple Knights are specialized warriors who guard the temples of God. The focus of their training is more close quarters combat vs. multiple opponents, rather than the word of God; thus they are able to handle more advanced weapons than the priests. Temple knights wear white mirdan armor (named for Mird, the long lost area where the first temples were built), carry a heater shield, talisman of God, and wield a halberd. The halberd's long reach allows the temple knight to strike at multiple foes with a single swing.
The lowest level are the acolytes, ordained men of the cloth who have not yet received much training. Acolytes serve as assistants during religious ceremonies and personal servants to higher level clerics. They believe in the word of God but without much proper instruction they are not yet able to perform miracles or wield much more than a humble dagger in battle.