The Last Supper as celebrated by Jesus and his disciples is significantly different than a pontifical high Mass at St. Peter's in Rome. Similarly, the early baptisms performed by immersion as described in the Acts of the Apostles is far different than the baptisms we see in our parishes today. In History of the Liturgy, Marcel Metzger shows how the essential form of the liturgy was fixed very early according to the tradition received from the Apostles. But the place given to biblical readings, teaching, singing, and ritual has varied through the course of the centuries. Here Metzger elaborates on some of the most important phases of these changes.