The hymn of the day is a congregational hymn

Hymn

A hymn is a type of song, usually religious, specifically written for the purpose of praise, adoration or prayer, and typically addressed to a deity or deities, or to a prominent figure or personification...

 that is centered on the theme of the lectionary

Lectionary

A Lectionary is a book or listing that contains a collection of scripture readings appointed for Christian or Judaic worship on a given day or occasion.-History:...

 texts for a given Sunday divine service.

The practice was developed by Lutherans

Lutheranism

Lutheranism is a major branch of Western Christianity that identifies with the theology of Martin Luther, a German reformer. Luther's efforts to reform the theology and practice of the church launched the Protestant Reformation...

 and is currently in use in other denominations

Christian denomination

A Christian denomination is an identifiable religious body under a common name, structure, and doctrine within Christianity. In the Orthodox tradition, Churches are divided often along ethnic and linguistic lines, into separate churches and traditions. Technically, divisions between one group and...

. According to Carl Schalk

Carl Schalk

Dr. Carl Flentge Schalk is a noted Lutheran composer, author, and lecturer. Between 1965 and 2004 he taught church music at Concordia University Chicago. During this time he guided the development of the university's Master of Church Music degree, which has since graduated more than 140 students...

, the hymn of the day came out of the singing of the gradual

Gradual

The Gradual is a chant or hymn in the liturgical celebration of the Eucharist for many Christian denominations. In the Tridentine Mass it was and is sung after the reading or chanting of the Epistle and before the Alleluia, or, during penitential seasons, before the Tract. In the Mass of Paul VI...

 which is sung before the epistle

Epistle

An epistle is a writing directed or sent to a person or group of people, usually an elegant and formal didactic letter. The epistle genre of letter-writing was common in ancient Egypt as part of the scribal-school writing curriculum. The letters in the New Testament from Apostles to Christians...

 reading.

Generally, it is used during the Word section of the liturgy

Liturgy

Liturgy is either the customary public worship done by a specific religious group, according to its particular traditions or a more precise term that distinguishes between those religious groups who believe their ritual requires the "people" to do the "work" of responding to the priest, and those...

, but can vary in its placement depending on which Lutheran hymnal

Hymnal

Hymnal or hymnary or hymnbook is a collection of hymns, i.e. religious songs, usually in the form of a book. The earliest hand-written hymnals are known since Middle Ages in the context of European Christianity...

 is used. For example, the Lutheran Book of Worship

Lutheran Book of Worship

Lutheran Book of Worship is a worship book and hymnal used by several Lutheran denominations in North America. It is often referred to by its initials as the LBW, and in the Evangelical Lutheran Church in America the LBW is sometimes called the "green book" as opposed to With One Voice, a...

(1978) suggests that the hymn of the day be placed either immediately before or after the sermon

Sermon

A sermon is an oration by a prophet or member of the clergy. Sermons address a Biblical, theological, religious, or moral topic, usually expounding on a type of belief, law or behavior within both past and present contexts...

. The newer Evangelical Lutheran Worship

Evangelical Lutheran Worship

Evangelical Lutheran Worship or ELW is the current, primary liturgical and worship guidebook and hymnal for use in the Evangelical Lutheran Church in America and the Evangelical Lutheran Church in Canada, replacing its three predecessors, the Lutheran Book of Worship , the Hymnal Supplemental , and...

(2006), however, only suggests its use after the sermon. The Lutheran Hymnal

The Lutheran Hymnal

The Lutheran Hymnal is one of the official hymnals of the Lutheran Church - Missouri Synod. Published in 1941 by Concordia Publishing House in St. Louis, Missouri, it was the LCMS' second official English-language hymnal, succeeding the 1912 Evangelical Lutheran Hymn-Book...

(1941) suggests that the hymn of the day precede the sermon with the Apostle's Creed preceding that.

Regardless of placement, some Lutherans, including Schalk, believe this to be the most important hymn in the worship service.