Justin Martyr described 2nd-century Christian liturgy in his First Apology (c. 150) to Emperor Antoninus Pius, and his description remains relevant to the basic structure of Christian liturgical worship: And on the day called Sunday, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succours the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need.
Thus, as Justin described, Christians assemble for communal worship on Sunday, the day of the resurrection, though other liturgical practices often occur outside this setting. Scripture readings are drawn from the Old and New Testaments, but especially the gospel accounts. Often these are arranged on an annual cycle, using a book called a lectionary. Instruction is given based on these readings, called a sermon, or homily. There are a variety of congregational prayers, including thanksgiving, confession, and intercession, which occur throughout the service and take a variety of forms including recited, responsive, silent, or sung. The Lord's Prayer, or Our Father, is regularly prayed. The Eucharist is the part of liturgical worship that consists of a consecrated meal, usually bread and wine.
Some Christian denominations practice closed communion. They offer communion to those who are already united in that denomination or sometimes individual church. Catholics restrict participation to their members who are not in a state of mortal sin. Most other churches practice open communion since they view communion as a means to unity, rather than an end, and invite all believing Christians to participate.
Some groups depart from this traditional liturgical structure. A division is often made between "High" church services, characterized by greater solemnity and ritual, and "Low" services, but even within these two categories there is great diversity in forms of worship. Seventh-day Adventists meet on Saturday, while others do not meet on a weekly basis. Charismatic or Pentecostal congregations may spontaneously feel led by the Holy Spirit to action rather than follow a formal order of service, including spontaneous prayer. Quakers sit quietly until moved by the Holy Spirit to speak.
Some Evangelical services resemble concerts with rock and pop music, dancing, and use of multimedia. For groups which do not recognize a priesthood distinct from ordinary believers the services are generally led by a minister, preacher, or pastor.Still others may lack any formal leaders, either in principle or by local necessity. Some churches use only a cappella music, either on principle (for example, many Churches of Christ object to the use of instruments in worship) or by tradition (as in Orthodoxy).
Worship can be varied for special events like baptisms or weddings in the service or significant feast days. In the early church, Christians and those yet to complete initiation would separate for the Eucharistic part of the worship. In many churches today, adults and children will separate for all or some of the service to receive age-appropriate teaching. Such children's worship is often called Sunday school or Sabbath school (Sunday schools are often held before rather than during services).