Before the reform of the Roman Rite at and following the Second Vatican Council, altar servers (often called “altar boys”) were exclusively males, usually boys of the parish or young men preparing for priesthood. As indicated in the window, they wore cassocks and surplices and their service at the altar included bringing the wine and water to the altar in small cruets (containers)and assisting with specific duties like holding the missal.
Those altar servers, then called a thurifers, would carry and swing the thurible, a metal vessel with chains, to burn incense during Mass or other liturgies, symbolizing prayers rising to God and showing reverence for the altar or Blessed Sacrament. The thurifer handles lighting the charcoal, loading the incense, and expertly swinging the thurible. The thurible with incense rising out of it is depicted in the lower window. Also represented in the window next to the thurible is a small bell indicating that an altar server is responsible for the ringing of bells at certain times during the liturgy.
Also, these altar servers learned Latin for participation in the Mass, primarily the prayers at the foot of the altar, as in the “Confideor” or responses like “Et cum spiritu tuo” (Latin meaning “and with your spirit”) or “Deo gratias” (Latin meaning “Thanks be to God”). These phrases are displayed in the window.