High altar at St. Peter’s Basilica, Vatican City. Photo credit: Ricardo André Frantz via Wikimedia Commons, CC BY-SA 3.0.
There are many reasons to celebrate the Mass ad orientem—facing the altar—including some rich symbolism about the End Times
By Joseph Shaw, Catholic Answers,
The subject of which direction the priest should stand while celebrating Mass has generated a great deal of attention since about the middle of the twentieth century. The celebration of Mass “facing the people” (versus populum) was officially encouraged after Vatican II, but the historic practice, of “facing East” (ad orientem), is still permitted in the reformed Mass and normative for the traditional Latin Mass.
Even before the Second Vatican Council, some important historic churches, notably St. Peter’s in Rome, had altars at which celebration facing the people was possible. In St. Peter’s (and also in the Basilica of the Holy Cross in Jerusalem), this was because the high altar was over an important holy place, which needed to be accessible from the nave of the church, via steps. The solution to the design problem was to allow the priest to celebrate facing east, toward the rising sun, from the apse side of the altar. This general arrangement was imitated (or anticipated) in some other ancient churches. …
