Christians gather regularly for worship, particularly on Sundays and on the great annual festivals. In these assemblies, their faith is directed to God in praise and prayer; it is also exposed to God for strengthening, deepening, and enriching. In the living encounter with God, the content and verbal formulations of faith are shaped, while in turn the tried and accepted teaching of the community provides the basis for each new celebration.

Worship contributed to the evolution of doctrine from the earliest days of Christianity. In the first decade of the 2nd century, the Roman investigator Pliny reports that the Christians meet “on a fixed day” and “recite a hymn to Christ as to a god.” The experienced presence of the risen and exalted Christ as living Lord is reflected even earlier in such New Testament texts as Matthew 18:20 (gathering “in his name” for prayer), Matthew 28:16–20 (Christ’s accompaniment of his Apostles in teaching and baptizing), 1 Corinthians 16:22 (the invocation Maranatha as “The Lord has come” or “Our Lord, come”), Philippians 2:9–11 (the bowing of the knee to Jesus and the confession from the tongue that he is Lord), and Revelation 1:4–18 (John’s vision, when he was “in the Spirit on the Lord’s Day,” of Christ standing among seven golden lamp stands and holding seven stars). The practice of worshipping Christ as the Lord, as early Christian and non-Christian sources indicate, was an important part of early Christian ritual, which played a central role in establishing the doctrine of his divine status. In the fierce debates of the 4th century, Athanasius maintained that the church’s worship of Christ established that he is fully God, for otherwise Christians would commit an unthinkable idolatry.

Influence also traveled in the other direction. From the beginning of the faith, doctrine contributed to the development of patterns of worship and has continued to do so. Theological reflection on Christ’s sovereignty in the present most likely led to belief also in his preexistence as the agent of the Father’s creative work from the very beginning. This belief then found expression in the hymns or other liturgical forms that are echoed at several places in the New Testament: 1 Corinthians 8:6; Colossians 1:15–20; and Hebrews 1:1–2, for example.

Church authorities have been keen to ensure that the language used in worship is doctrinally orthodox. The Apostolic Tradition, an early church order, sets out a sample prayer for a newly ordained bishop to use at the Eucharist, saying that it is not necessary that he use exactly these words, “only let his prayer be correct and orthodox.” A similar concern led some North African councils around the year 400 to discourage new compositions. In the Middle Ages, the great metropolitan bishoprics—and even, in the case of Charlemagne, the imperial court—sought to standardize liturgical forms in their areas. The advent of printing made this easier, and the Protestant reformers issued books for the purpose, either laying down verbally the entire content of the service (as in the Church of England’s Book of Common Prayer) or publishing “directories” that set out in some detail the principles according to which the minister should conduct the service (as sometimes in the Reformed or Presbyterian case). Following the Council of Trent, the Roman see produced a series of books that regulated the words and gestures of the rites down to the last detail (Breviary, 1568; Missal, 1570; Pontifical, 1596; and Ritual, 1614). Less bookish churches have relied more on individual ministers, assuming the fundamental doctrinal soundness of the ministers or their recurrent inspiration by the truth of God or both.

Wherever sermons are preached to the congregation, a special responsibility rests on the preacher to build the local community up in the Christian faith. The theological assumption is that the entire liturgy is both a school and the feast of faith: in the same act, believers both learn and celebrate the transgenerational faith of the Church into which they grow. This assumption was the motivation of the liturgical revisions and renewals attempted in many Western churches in the second half of the 20th century. An outstanding example is provided by Eucharistic Prayer IV in the Roman Missal of 1969–70, which has been borrowed and adapted by several other churches. Here the words and the ritual actions allow a reappropriation of the entire story of salvation:

Father in heaven, it is right that we should give you thanks and glory: you alone are God, living and true. Through all eternity you live in unapproachable light. Source of life and goodness, you have created all things, to fill your creatures with every blessing and lead all men to the joyful vision of your light. Countless hosts of angels stand before you to do your will; they look upon your splendor and praise you night and day. United with them, and in the name of every creature under heaven, we too praise your glory as we say: Holy, holy, holy Lord, God of power and might, heaven and earth are full of your glory. Hosanna in the highest. Blessed is he who comes in the name of the Lord. Hosanna in the highest. Father, we acknowledge your greatness: all your actions show your wisdom and love. You formed man in your own likeness and set him over the whole world to serve you, his creator, and to rule over all creatures. Even when he disobeyed you and lost your friendship, you did not abandon him to the power of death, but helped all men to seek and find you. Again and again you offered a covenant to man, and through the prophets taught him to hope for salvation. Father, you so loved the world that in the fullness of time you sent your only Son to be our Savior. He was conceived through the power of the Holy Spirit, and born of the Virgin Mary, a man like us in all things but sin. To the poor he proclaimed the good news of salvation, to prisoners, freedom, and to those in sorrow, joy. In fulfillment of your will he gave himself up to death; but by rising from the dead, he destroyed death and restored life. And that we might live no longer for ourselves but for him, he sent the Holy Spirit from you, Father, as his first gift to those who believe, to complete his work on earth and bring us the fullness of grace. Father, may this Holy Spirit sanctify these offerings. Let them become the body and blood of Jesus Christ our Lord as we celebrate the great mystery which he left us as an everlasting covenant. He always loved those who were his own in the world. When the time came for him to be glorified by you, his heavenly Father, he showed the depth of his love. While they were at supper, he took bread, said the blessing, broke the bread, and gave it to his disciples, saying: Take this, all of you, and eat it: this is my body which will be given up for you. In the same way, he took the cup, filled with wine. He gave you thanks, and giving the cup to his disciples, said: Take this, all of you, and drink from it: this is the cup of my blood, the blood of the new and everlasting covenant. It will be shed for you and for all men, so that sins may be forgiven. Do this in memory of me. Let us proclaim the mystery of faith: Christ has died, Christ is risen, Christ will come again. Father, we now celebrate this memorial of our redemption. We recall Christ’s death, his descent among the dead, his resurrection, and his ascension to your right hand; and, looking forward to his coming in glory, we offer you his body and blood, the acceptable sacrifice which brings salvation to the whole world. Lord, look upon this sacrifice which you have given to your Church; and by your Holy Spirit, gather all who share this one bread and one cup into the one body of Christ, a living sacrifice of praise. Lord, remember those for whom we offer this sacrifice, especially N. our Pope, N. our bishop, and bishops and clergy everywhere. Remember those who take part in this offering, those here present and all your people, and all those who seek you with a sincere heart. Remember those who have died in the peace of Christ and all the dead whose faith is known to you alone. Father, in your mercy grant also to us, your children, to enter into our heavenly inheritance in the company of the Virgin Mary, the Mother of God, and your apostles and saints. Then, in your kingdom, freed from the corruption of sin and death, we shall sing your glory with every creature through Christ our Lord, through whom you give us everything that is good. Through him, with him, in him, in the unity of the Holy Spirit, all glory and honor is yours, almighty Father, for ever and ever. Amen.

So comprehensive was this prayer that the Catholic bishops of France made it the basis for a short popular catechism, Il est grand, le mystère de la foi: prière et foi de l’église catholique (1978; “It Is Great, the Mystery of the Faith: The Prayer and Faith of the Catholic Church”).

Hymns have been significant vehicles of the Christian faith from the earliest days. They have been sung particularly in the daily offices of the Orthodox and Roman Catholic churches, and they have figured prominently in the Sunday worship of many Protestant churches, especially the Lutheran and Methodist. Congregational singing is appropriate to the “bodily” character of Christianity, in both the physical and the social senses of the word, as it permits the members of the Body of Christ to engage “with one heart and one voice” in the worship of God (Romans 15:5–6).