Some men and women are born with lower sex drives, i.e. more 'ideologically' driven than sexually driven. Due to the nature of male and female sexuality there will be a LOT of men that just don't get to breed for various reasons. The church or Abbey is a safe space for these men. It's not just a safe space but a space that makes non sexually reproducing men useful for the community. When religion isn't subverted men of the cloth essentially become fathers for the entire community using their sexual energies towards studies in morality, spirituality, history, agricultural studies, beer making, intellectualism, letters, academics, etc. Women that don't breed can also access the church through the convent. It gives people that are left out of the breeding game an option to still have a meaningful and fulfilling life. And more importantly it keeps these non breeders away from degeneracy or other acts that hurt the community. If you don't have something productive for non breeding men to do they may use that energy and time to overthrow the community.