Confession Booth I is built in the Church for 6 Wooden Plank and 8 Bronze Nails. +4 church quality. Unlocked by Church Furniture I. Its construction site needs Building mastery 2: below that, hits do nothing.
It adds 4 to church quality. More elaborate sermons need a higher church quality. Each new best church quality counts towards the Sacred Interior inspiration. Church Furniture I also unlocks Church Shrine I.