Augustine's Liturgical Argument:

So, I'm poking through Augustine, and he makes an interesting argument against Pelagians, who taught that the grace of God working in us was merely the knowledge, the intellectual enlightenment that makes us good, once we acknowledge it. As for God giving the grace for us to accomplish that which he commands, that seems to the Pelagian to annul our free will. So much for Church history.

Augustine argues against him by saying that if Pelagius is right, our prayers in the churches are in vain:

Destruunt etiam orationes, quas facit Ecclesia, sive pro infidelibus et doctrinae Dei resistentibus, ut convertantur ad Deum; sive pro fidelibus, ut augeatur in eis fides, et perseverent in ea. (Ex Augustini Libro De Haeresibus ad Quodvultdeum, Haeresis 88)

Translation: (By their doctrine) prayers indeed are done away with, which the Church makes, either for the unbelievers and those resisting the doctrine of God, that they be turned to God, or for the faithful, that they may be increased in their faith, and persevere in it.

The key interest: he argues from the liturgy to the theology. The Church has always prayed for these things, and therefore they must be good. Any doctrine that conflicts with the ancient liturgical traditions of the Church must be wrong. The liturgy serves as a rule of faith.

All the more reason, I think, for us to be conservative in things liturgical.