The Latin phrase “Lex Orandi, Lex Credendi” is generally translated as the law of prayer is the law of belief. The reverse is also true; the law of belief is the law of prayer. But what does it mean?
The “Law of Prayer” is a reference to the prayers the worshipping church. So one way of looking at it is that the way we worship reflects the way we believe, and the way we believe is reflected in our worship. This seems reasonable and straightforward. But how does this work in practice?
A great many Protestant communities create their own hymnals. Other Protestant bodies share hymnals across denominational lines. The reason for the variety of Protestant hymnals is they reflect differences in doctrine. Hymnals from a Presbyterian tradition will have a different collection of hymns than a hymnal from the Reformed, which would be different from the Wesleyan or Lutheran hymnal.
Within the Lutheran community in America, there are quite a few different denominations, each with different hymnals reflecting their differing approach to Scripture and differing understanding of the Lutheran Confessions. The hymnals contain different selections of hymns and different liturgies — both of which reflect differences in belief. Even when different hymnals contain the same hymns, there may be differences in translation, or the hymns may be rewritten to reflect changes in both doctrine or societal norms, such as gender-neutral language.
We still have not exhausted the complexity of our discussion. Whereas the older hymnals tended to have just a few different musical settings of the same liturgies, the newer hymnals not only contain different musical settings, but actual variations between the liturgies. And within liturgical variation are different propers (the changeable parts of the liturgy), and occasionally there may even be differences in the ordinaries (the parts of the service that are supposed to stay the same from week to week). The liturgical variations within the service are presented in multiple columns. Thus, even within the same Protestant denomination there can be wide variation in the conduct of the service from one church to another — and between churches that use the same liturgical settings.
I contend that the beliefs of a church body are reflected in their choice of hymnal. If this is true, then the change of hymnals that tend to take place each generation, in that it changes the worship of the church, reflects an actual change in doctrine. And when a hymnal contains not merely different liturgical settings, but actual liturgical variations, this reflects the doctrinal disagreements that exist within that church body.
Another way to view this change is to look at the differences between the older and the newer catechetical (or religious instructional) material. Whereas hymnals tend to change each generation, catechetical material seems to change less often. Within the Lutheran Church, catechesis is generally represented by Luther’s Small Catechism, which doesn’t change. However, the explanation of the Small Catechism is usually appended in the same volume. These explanations are quite different between the different Lutheran bodies, and even between versions published by the same Lutheran body.
The most recent Small Catechism with Explanation for the LCMS was published in 2005. The previous version was first published in 1943. There are distinct differences in the Explanations between the two versions (explanations which are presented in question and answer form). In some cases, the differences reflect societal changes. In the 2005 edition the first question asked is “What is a Christian?” This question was not included in the 1943 version, which indicates a considerable societal change in the intervening 60 years. There are also differences in the questions asked and the answers given. These are subtle, yet significant differences, differences that are debated by pastors of the LCMS.
Lest you think this is a tirade against Protestants, the Roman Catholics have their own issues. It is clear that there is a distinct difference in Roman Catholic worship before and after Vatican II. This is not only because the Vatican allowed the mass to be celebrated in languages other than Latin, but because the actual liturgy changed. There are changes in the prayers of the church in the Latin rite versus the post-Vatican II vernacular rite. This can be demonstrated by the furor that developed when Pope Benedict XVI relaxed the rules governing when and where the Latin rite can be held, primarily because the old Latin rite contained a prayer calling for the conversion of the Jews, a prayer than had not been carried forward into the post-Vatican II rite.
While the Roman Catholics will never formally admit the church has changed (and why would we expect them to), it is clear that it has changed over time — if for no other reason than the change in the attitude towards the Eastern Orthodox. Meanwhile, the Eastern Orthodox Orthodox Church will often say that it hasn’t changed since the days of the apostles. Yet this isn’t precisely true, either.
It is clear that the Eastern Orthodox liturgy has changed over the years. This can be demonstrated by perusing Ante-Nicene Fathers, Volume VII, containing The Liturgy of St. James; The Liturgy of the Holy Apostle and Evangelist Mark; and The Liturgy of the Blessed Apostles. Not only are these clearly different from The Liturgy of St. Basil and The Liturgy of St. John Chrysostom used today, but they show evidence of interpolations over time. So the question is why did the Liturgy change; and can it be said that these changes reflect actual doctrinal changes?
The simple answer is yes, the liturgies changed because the doctrine of the church changed. Or rather, as the doctrine of the church was set forth by the ecumenical councils, these definitions were incorporated into the liturgy of the Church. So whereas the early church allowed for a greater variety of expressions of Christianity, the later church found it necessary, in response to heresy, to define the faith more precisely. Thus, while the church in Asia Minor had a certain millenialist quality, this doctrinal option was closed off when the Second Ecumenical Council added the following phrase to the Creed: “whose kingdom shall have no end.”
It is clear that different areas of the Roman Empire developed different liturgies, which appear to be based on common prototypes. This is evidenced in part by the similarities between the different church orders passed down to us as the Didache (~50 A.D.), the Didascalia Apostolorum (~230 A.D.), the Apostolic Traditions (of Hippolytus, ~215 A.D.), and the Apostolic Constitutions (~375 A.D.). In addition, the different liturgical families contain much the same basic structure and content. The similarity within the liturgical families is even more pronounced. The Liturgy of St. James is roughly comparable to the Liturgy of St. Basil and the Liturgy of St. James; the differences primarily being that some of the more flowery language of the Liturgy of St. James has been condensed and simplified in the later liturgies.
As an Eastern Orthodox Christian, I can follow the Liturgy of St. James, and recognize nearly all of it. But I can also say that when I first read it, I noticed some commonality between it and what Lutheran’s sometimes call the “Common Service”, or what may be more generally known as the Western Rite. This demonstrates that the Eastern and Western Rites are derived from a common source. One difference I note is the absence of the Epiclesis in the Western Rite, which is the Eucharistic prayer which calls for the Holy Spirit to change the bread and the wine into the body and blood of Christ.
It is not always clear why the epiclesis is missing from the Protestant version of the Western Rite. However, we may infer this from the movement of the epiclesis in the Roman Catholic rite to a place prior to the so-called words of institution, which in the western sacramental Churches, is the point at which the bread and wine become the body and blood of Christ. In the Eastern Church, the definition of when this occurs is left open, but is definitely said to have occurred once the epiclesis has uttered.
What does this all matter, anyway? To the average churchgoer, not much. But in the early church, and among today’s flea-picking theologians, it matters a great deal. The simply movement of the epiclesis within the liturgy represents a profound theological change. In the East there is an appreciation of mystery, and a sense that not everything requires or is even subject to intellectual analysis. In the West, the question of when exactly the bread and wine becomes the body and blood of Christ is not only a matter for intellectual analysis, but the answer to that question actually changes the liturgy.
Lex Orandi, Les Credendi. The way we worship reflects the way we believe. Thus the difference between the so-called contemporary service, what the U.S. Military would call a general Protestant service, and a liturgical service represent fundamental differences in doctrine. Likewise the differences between the Western Rite and the Eastern Rite are reflective of differences in doctrine.
I said all this as preparatory to asking this question: Does the use of the Western Rite in Eastern Orthodox Churches reflect an actual difference in theology?
 For example, the latest hymnal of the Lutheran Church-Missouri Synod (LCMS) contains remarkably few hymns written by Luther himself. What this means I leave to others to determine.
 A Lutheran pastor once mentioned that an analysis of the theological differences between the various versions of the Small Catechism’s explanations would make a good subject for a Ph.D. dissertation, which is why I choose not to delve into the subject here.
 The editor’s comments in ANF-7 describe this phrase being added to the creed to combat the errors of one Marcellus of Ancyra. Among other things, the Marcellians appeared to hold to the impermanence of the Kingdom of the Son, something they shared in common with the chiliasts, those who held to an earthly temporal Kingdom prior to the permanence of the heavenly Kingdom.
 See ANF-7, pp. 793-794
 See ANF-7, p. 791
 The Epiclesis, from the Liturgy of St. James:
Then, bowing his neck, [the priest] says:—
The sovereign and quickening Spirit, that sits upon the throne with Thee, our God and Father, and with Thy only-begotten Son, reigning with Thee; the consubstantial and co-eternal; that spoke in the law and in the prophets, and in Thy New Testament; that descended in the form of a dove on our Lord Jesus Christ at the river Jordan, and abode on Him; that descended on Thy apostles in the form of tongues of fire in the upper room of the holy and glorious Zion on the day of Pentecost: this Thine all-holy Spirit, send down, O Lord, upon us, and upon these offered holy gifts;
And rising up, he says aloud:—
That coming, by His holy and good and glorious appearing, He may sanctify this bread, and make it the holy body of Thy Christ.
And this cup the precious blood of Thy Christ.