Question: Why do parishes have the Blessed Sacrament in a separate room?
Answer: While many Catholics of a certain age have memories of the Blessed Sacrament being housed in the tabernacle on the high altar of the church, many parishes in the decades since the Second Vatican Council have chosen to build a separate space — a reservation chapel — where the Blessed Sacrament is kept. Although this practice is not universal, it is in keeping with the guidance offered by the US Bishops in their document Built of Living Stones (see nos 77-78). The goal is to create a space that is separated from the nave and sanctuary, but which is “integrally connected with the church” which can foster “reverence and can provide the quiet and focus needed for personal prayer.” This can be especially important for communities that have continuous eucharistic adoration, allowing people to come and pray in a space separate from the normal activities of parish life.
The practice of reserving the Eucharist in a separate space — or in a dignified location away from the altar where Mass is celebrated — is that it emphasizes the importance of the liturgy itself, which is the “source and summit” of the life of the Church.
As with many things in the Church, the practice of placing the tabernacle in the sanctuary or in a separate chapel is not universal (as can be seen in visits to historic churches in Rome and other places). The important thing is that as communities question where to place the tabernacle, they listen to the voice of the Church, explore the ancient and varied liturgical tradition of the Church, consider the needs and life of the community, and also take into account the architecture and limits of the spaces they might already have.