What is Ad Orientem? The phrase Ad Orientem, which means “Toward the East“, refers to the practice of the priest celebrating the Mass facing the liturgical East, which is represented by the crucifix behind the altar. We are generally used to the people facing the crucifix but the priest facing the people. Ad Orientem means that the priest and people are all facing the crucifix together, with the priest leading the people of God toward the Lord.
Ad Orientem is the traditional way the Mass was celebrating for hundreds of years. After Vatican II, priests had the option of celebrating Mass Ad Orientem or Versus Populo (toward the people). I believe this ancient practice is very beneficial and helps draw both the priest and people deeper into the mystery of the sacrifice of Christ that we offer at every Mass.
When the priest faces the people (Versus Populo), it is easy to assume the priest is always talking to the people. However, when the priest is facing the crucifix, it is clear that he is talking to God. This is the most important reason why Ad Orientem is an important way of celebrating the Mass, because it helps make clear that the priest is talking to the Father as he offers the prayers of the Eucharist.
Here is a simple picture that helps clarify this idea: