Since I’m teaching a class on Sacramental Theology this term, I’ve been thinking once again about how Christian ritual serves as a source and expression of Christian belief. Rivers of ink have been spilled on this question, but they are worth wading into every once in a while, trusting that we have changed sufficiently that we might learn something new.
Much of liturgical scholarship cheerfully refers to the church’s liturgy as its primary theology, or cheers on the importance of liturgical study by citing Prosper of Aquitaine (390–455). “Lex orandi, lex credendi” is practically emblazoned across every lintel of the halls of liturgical studies: “the law of prayer is the law of belief.” How we pray matters. It forms us, it structures our common belief, and is therefore a worthy object of study in itself.
But Prosper’s pithy bumper sticker ought to peak our interest. Why, after all, is this a lex? What law or principle does prayer put forth? Why doesn’t he just say “belief is established in prayer,” which is what we mean when we cite him, at least most of the time.
It is worth noting that Prosper’s quotation is making a somewhat more complex point. Specifically, he sees the liturgy as grounding universal faith because he believes that it is both of apostolic origin and universal in its nature. These two characteristics make it, he argues, into an unimpeachable guide for theological reflection.
The full citation from which our motto is taken is this:
Alongside of the inviolate law of the most blessed and apostolic seat, by which our most pious fathers, rejecting the arrogance of pestilential novelty, have taught [us] to attribute to Christ’s grace both in its beginnings in good will, and in the commendable progress of zeal, and even in being preserved in these efforts to the end, let us consider as well the supplications of the priestly rites, which having been received from the apostles, are celebrated in the same way in the entire world and throughout the whole catholic church, such that the law of prayer establishes the law of belief.”
And so, for Prosper, liturgy is a source for reflection because it is apostolic and universal. This is not very far from the equally famous canon laid down by St. Vincent of Lérins: true Christian doctrine is that believed “semper, ubique, et ab omnibus” (always, everywhere, and by all). Vincent augments this description by a recognition that Christian doctrine grows, but it must do so in continuity with what preceded it.
Of course, no contemporary liturgist can assume this kind of universality or direct apostolic authorship for the liturgy, at least as understood to mean the Sacramentary or other ritual texts. We simply have too much good historical research detailing the development and diversity of rites to do so.
But here, perhaps, paying closer attention to Prosper’s word choices might help us: he speaks of the lex supplicandi, that is, the law of supplication. The church’s belief, then, is grounded in something that is universal and is received from the apostles: a stance towards God, which is widely expressed in Christian practice through the posture we call orans, “beseeching.” The church always stands with hands outstretched, entreating God for that which God has promised to give, already living out the gift of a new life that it cannot ever earn.
This posture has been made visible in all kinds of Christian living. In the Rule of St. Benedict, each newcomer pleads that God will “receive her as he has promised that she may live.” (RB 58: 21; Ps. 118:116). In turn, the community is called to receive its abbot, visitors, and each other “as Christ” that is, as the one who has already received them, and to whom grateful response is due.
In the works of Lent, the church stands before God and asks his mercy directly (prayer) in the body (fasting) and in reception of neighbors (alms). At Easter, the whole story of God’s mercy is rehearsed for the purpose of building up the church and adding new members to the body of God’s mercy.
As we enter into another Holy Week and bring our Lent to a close, it is worth considering to what extent the church’s posture, its lex supplicandi, has formed our lives and our communities. And for those of us in the position of teaching, planning liturgies, writing hymns or homilies, or producing other works of secondary theology for the church, we ought to once again ask ourselves how well these serve the church that stands as the recipient and sign of God’s mercy.
 “Praeter beatissimae et apostolicae sedis inviolabiles sanctiones, quibus nos piissimi patres, pestiferae novitatis elatione dejecta, et bonae voluntatis exordia, et incrementa probabilium studiorum, et in eis usque in finem perseverantiam ad Christi gratiam referre docuerunt, obsecrationum quoque sacerdotalium sacramenta respiciamus, quae ab apostolis tradita, in toto mundo atque in omni catholica Ecclesia uniformiter celebrantur, ut legem credendi lex statuat supplicandi.” (Prosper of Aquitaine, Praeteritorum sedis apostolicae episcoporum auctoritates, de gratia dei et libero voluntatis arbitrio, ch. 8. PL 51, col. 0209c.)
 Both are found in Vincent’s Duo Commonitoria, (Migne PL 50.0640; 0667–68).