As you know, our 5:00 Mass at St. John's is celebrated ad orientem (or, "towards the east") and has been for a couple of years now. One of the most important of the Church Fathers (the leaders of the Church which lived in the three to four centuries after the Apostles) was St. Basil of Caesarea (AKA St. Basil the Great). He died in 379. Of his many writings, the New Liturgical Movement blog (a great resource for all things liturgical, BTW) recently highlighted a great nugget on why celebrating the Mass ad orientem (i.e. towards the East) is an important part of Christian Tradition. You can read the entry here: St. Basil the Great on "Ad Orientem".