Edward Burbidge: Liturgies and Offices of the Church, 106ff.

Additional Note A, ON THE CANON, 106-111. The varied sacramentaries are noted and discussed--Ambrose’s (4th century), Leo’s (5th), Gelasius’s (5th) and Gregory’s (late 6th century). The Celts had their own services for at least 300 years before Augustine the Lesser and his Roman cohorts arrived in Kent. Originally, the Eucharistic was a “sacrifice of praise and thanksgiving” (the Eucharist, giving thanks), a memorial of the redemption by Christ’s death, burial and resurrection. They "pled the merits of Christ." That is, remarkably distant from the medievalist concept. Slowly and surely, the idea of “sacrifice” obtains a “pay-back” sense. I’m offering this, Lord, not just in memorial of Thy Son's redemption, but in the hopes of a pay-back (my words). In time, it slips towards a “propitiatory” sacrifice. That gets a steroidal lift from Aquinas. The bird that was hatched at Lateran Council 4 in 1215 will display its full, preening, and parading plumage in Trent, like a strutting peacock. Rome’s Masses are still merit-pile-ons for the living and the dead, detracting from Christ Himself and insulting His definitive and final work.

Every church has a liturgy. It is impossible to not have one. The question is: what kind, for starters?