What are the memorized lines people are reciting in church?

For the Catholic Church, there is the Order of Mass, which details all of the common parts of the Mass.

It is available online as a PDF:

• The essential version
• The version with annotations

If the reader were to attend an actual Mass in the United States and Canada, the common parts of the Missal are nearly always available as booklets in the pews.

The longest texts that are recited (or sung) in common are the Gloria (Glory to God) and the Nicene-Constantinopolitan Creed (or, less commonly, the Apostles’ Creed). These are not Scripture, but an ancient hymn and an ancient profession of faith. (The Gloria is said only on Sundays outside of Lent and on festive days; the Creed is said only on Sundays and solemnities—that is, major feast days like Christmas.)

Other texts that are recited or sung in common include (sometimes) the Confiteor (“I confess”), the Sanctus (the “Holy, Holy, Holy,” which is said in between two portions of the Eucharistic Prayer), the Lord’s Prayer (“Our Father”—the one only of these that is actually Scripture quoted word-for-word) and the doxology (“For the kingdom, the power, and the glory are yours....”), the Agnus Dei (“Lamb of God”), and the Domine, non sum dignus (“Lord, I am not worthy”).

Based on the website of the Lutheran Church Missouri Synod, it seems the Lutheran service is rather similar in form to the Catholic Order of Mass. (Disclaimer: I am a Catholic priest, and have never been to an actual Lutheran service.) I could not find the actual texts, but there is a part-by-part description of the service on the website. Like Catholics, Lutherans (at least the Missouri Synod Lutherans) recite the Gloria, the Creed and the Sanctus together.

Liturgical Christians

I grew up as a member of the denomination that is now known as the Evangelical Lutheran Church in America (ELCA), and attended an Episcopal Church when I was in college.

The spoken or sung portions of the service that are not hymns or customized prayers is called the "liturgy".

Christians that have a liturgy as part of their church services (such as Roman Catholics, Episcopalian/Anglicans, and Lutherans, and to a lesser extent Presbyterians and Methodists) are called "liturgical Christians", although the term is sometimes restricted to Protestants who are liturgical Christians.

What Is The Protestant Liturgy?

The Protestant liturgies are derived from one of several "vernacular" (i.e. in the local language rather than Latin) translations of the Roman Catholic mass as it existed at the time of the Protestant Reformation, with very slight substantive alterations (most notably the omission of the word "transubstantiation" from the language related to the sacrament of communion and the omission of several of the sacraments than are found in the Roman Catholic church).

There were three main translation efforts involved: One, originally into German, by the Lutherans; one in English by the Anglicans (this is closer to the Catholic mass as the Anglican church left Roman Catholicism mostly so the King could divorce as opposed to out of deep ideological disputes with the Pope); and a third by the Calvinists (whose successors in the U.S. include Presbyterians and the "Reformed" church).

The Methodist Church split off from the Anglican Church about two centuries after the Anglicans split from the Roman Catholics and diluted many of the Anglican church's more high church practices. So its liturgy is derived from the Anglican one. (The Episcopal Church is the Anglican church in the United States that rebranded itself after the American Revolution when identifying with the English was out of favor.)

Following Vatican II and other reforms in the Roman Catholic Church, starting around the 1970s, when vernacular translations of the Roman Catholic mass from the historical Latin version were much more widely used, many people were surprised to learn how similar that had remained despite roughly 500 years of separation. (This is also the historical moment that Latin began its long and relentless decline in the high school and higher educational curriculum.)

Other Protestant denominations such as Presbyterians and Methodists use somewhat abbreviated liturgies (and are much less likely to sing them).

In "high church" liturgical Protestant Congregations, the liturgy is sung with a pastor or a "cantor" (i.e. someone, not necessarily ordained, who sings the liturgy if the pastor can't carry a tune) leading the liturgy after which the congregation responds. Roman Catholics and some high church liturgical Protestants not only sit and stand but also kneel and sometimes genuflect at designated moments in the worship service.

In the more common "low church" liturgical Protestant Congregations, the liturgy is spoken with the pastor leading and the congregation responding, kneeling is dispensed with, incense is not used during the service, and genuflection is also omitted.

Locating the liturgy

Most liturgical churches have copies of the liturgy in a hymnal or prayer book available at every pew. Usually a church bulletin points you to the right page to read from although it goes by very fast. Finding the right page is trickier than it seems because there are several seasonal variations on the liturgy that are subtly different and you have to make sure you are reading the right version for the current service.

Some Congregations and Parishes, particularly in locations or at times when they are prone to having newcomers, will publish a church bulletin that actually reproduces all of the liturgy language that the members of the congregation need to recite and the text of all the hymns that will be sung in the bulletin itself, rather than merely a list of what parts of the liturgy will be used (which varies somewhat with the season of the church over the course of a year) and what hymns will be sung.

Congregations of liturgical Christians and some Roman Catholic Parishes have also emulated the usual practice of large non-denominational churches of displaying the liturgy and the text of the hymns on large screens visible to the congregation.

While many regular church goers in all forms of Christianity that use a liturgy memorize the liturgy, the social expectation that you memorize it is much greater in the Roman Catholic church than in most Protestant liturgical churches. I assume, but do not know, that this is a part of the Confirmation process that adolescents go through which is more rigorous in the Roman Catholic church than for Lutherans. (The Roman Catholic Catechism is the size of a thick paperback novel; the Lutheran version runs about 80 mini-sized pages.)

The Lutheran Liturgy

ELCA Lutherans use hymnals including one called the Lutheran Book of Worship (I grew up with the green 1978 edition with gold lettering on the exterior shown above) that contains both the liturgy which has page numbers in the front portion, and hymns which have sequential hymn numbers and are placed in order of season and purpose in the back portion of the book.

In the Evangelical Lutheran Church in America, the LBW is sometimes called the "green book", as opposed to With One Voice, a blue-covered supplement; or the previous Service Book and Hymnal, bound in red; or The Lutheran Hymnal, which is also bound in red, but with a simple gold cross.

The Lutheran Book of Worship was drafted as a joint effort of four North American Lutheran denominations including the ELCA and the Lutheran Church - Missouri Synod (LCMS) starting in 1965, although the LCMS dropped out of the venture right around the time it was completed and produced an alternative in 1982.

You can get a used copy on Amazon.com for about $8, or buy a new one from the Augsburg Fortress Press. As far as I know, there is no free version online. But, you can hear some of it sung in high church fashion in this You Tube video.

The Lutheran Church - Missouri Synod subsequently adopted the Lutheran Service Book in 2004, published by Concordia Publishing House, for which a substantial sampler with many portions of the liturgy is available. The Lutheran Service Book retains more of the smattering of Latin words held over from the Roman Catholic Latin mass than the ELCA.

Lutheran church music is usually melodically simple (although some efforts were made in the LBW to adopt a bit more musical complexity) and h*m*phonic (i.e. a single melody supported by simple cords, as opposed to having the intertwined melodies of polyphonic music).

Many of the most well known Lutheran hymns were adapted by Martin Luther and his early colleagues from decidedly low brow 16th century German drinking songs in the era before it became the government sanctioned established church for most of Northern Europe.

The Episcopal/Anglican Liturgy

The Episcopalian liturgy is contained in a book called the Book of Common Prayer (created independently of the Lutheran liturgy) which has the most familiar version of the liturgy and turns of phrase to most Americans because the Book of Common Prayer also forms the basis of the liturgies of several other denominations of Protestants in the United States (usually with simplifications from the Episcopal/Anglican version and usually rejecting the more modern additions to it that for example reference interstellar space in some prayers), most notably the Methodists.

The most stereotypical version of the wedding service, for example, is from the Book of Common Prayer.

The most recent edition of the Book of Common prayer is available online here.

Episcopalians generally have a separate hymnal from the Book of Common Prayer, which can make for quite a bit of juggling of books during a service.

For what it is worth, the Episcopal musical arrangements of the liturgy and hymns are more sophisticated musically (and choice of language is also more sophisticated in many cases) than the Lutheran, Presbyterian or Methodist versions which are either second order translations from an intermediate language that was in turn translated from the original Latin, or were deliberately dumbed down, as the Methodists did, to accommodate the limitations of life on the American frontier.

Liturgical v. Non-Liturgical Protestants

Many Evangelical and "fundamentalist" churches do not use a liturgy, a practice that dates back at least to the Puritans in the 1600s who rejected the liturgy on the grounds that it was part of the Roman Catholic tradition accumulated over time, rather than being something that was used by Christians in the early Christian church before it was organized into a more or less unified bureaucratic organization.

For liturgical Christians, however, the liturgy and traditions around the seasons of the church calendar (see below) in which it is embedded provide a comforting rhythm of life and connection to an ancient shared Christian heritage.

Roman Catholics and some very high church Lutherans and Episcopalians also celebrate some "Saint's Days".

For them, rather than representing a corruption of the early church, the Western religious tradition provides an answer to the question "what has God been up to since the 4th century?", which is a vacuum without the Roman Catholic and successor Protestant church tradition such as the liturgy, holy orders, and saints.

• The main seasons of the church calendar are, in order, Advent (the month before Christmas), Christmas (Christmas until early January), Epiphany (early January until Mardi Gras), Lent (40 days before Easter), Holy Week (the week before Easter), Easter (in the Spring but floating a bit to coordinate with the timing of Passover in the Jewish lunar calendar), and Pentecost (one of the longer seasons starting in the summer 40 or 50 days or so after Easter).