The sacristy adjacent to the church and the Sub Rosa room are areas of both architectural and cultural fascination. The eight-sided columns offer a sense of Byzantine elegance, a deviation from typical Gothic or Romanesque motifs, while the complex vault ribbing in the ceiling showcases the pinnacle of artisanal craftsmanship of that era.

The entrance inscription, "Domus Lavretana Verblin Carnatie Virgine nath Venerat lanla popVLI probouk Vr," indicates that the sacristy may have specific religious importance, perhaps devoted to the Virgin Mary or "Virgo Lauretana." This makes the space not merely an architectural achievement but also a significant site of spiritual and local reverence.

"Sub rosa" literally translates to "under the rose," signifying secrecy or confidentiality. This Latin phrase has roots in ancient Roman traditions where a rose was hung over banquet tables to symbolize that matters discussed should remain confidential. This meaning extended into the Middle Ages, where roses adorned rooms where confidential meetings were held, and even in Catholic confessionals. The symbol originates from Amor, who received a rose from Venus and dedicated it to Harpocrates, the god of silence, to keep lovers' secrets safe. This adds an extra layer of intrigue to the Sub Rosa room, implying that it might have been a setting for secret or sacred activities, a notion that enriches its already multi-faceted significance.

In essence, the sacristy and the Sub Rosa room are not just marvels of architecture but intricate tapestries of spiritual, cultural, and even secretive dimensions that add depth to the church's overall heritage.