format laid out by the dictates of the denomination. Some churches are "lay led" with members of the congregation taking turns guiding the service or simply following format that has evolved over time between the active members. More commonly, an ordained minister will preach a sermon (which may cover a specific topic, or as part of a book of the Bible which is being covered over a period of time). Depending on the church, a public invitation follows whereby people are encouraged to become Christians, present themselves as candidates for baptism or to join the congregation (if members elsewhere), or for other purposes. A few begin their church services with the ringing of a bell (or a number of bells); a current trend is to have an introductory video which serves as a "countdown" to the beginning of the service. The service usually involves the singing of hymns, reading of scripture verses and possibly a psalm. If the church follows a lectionary, the sermon will often be about the scripture lections assigned to that day. Eucharistic churches have usually Holy Communion either every Sunday or several Sundays a month. Less liturgical congregations tend to place a greater emphasis on the sermon. Many churches will take up a collection of money (offertory) during the service. The rationale for this is taken from , , and . But some churches eschew this practice in favor of voluntary anonymous donations for which a box or plate may be set up by the entrance, or return-address envelopes may be provided that worshippers may take with them. Offering through the Internet has become a common practice in many evangelical churches. On occasion, some churches will also arrange a second collection, typically occurring after Communion, for a specific good cause or purpose. Some churches offer Sunday school classes. These will often be for younger children, and may take place during the whole of the service (while the adults are in church), or the children may be present for the beginning of the service and at a prearranged point leave the service to go to Sunday school. Some churches have adult Sunday school either before or after the main worship service. Following the service, there will often be an opportunity for fellowship in the church hall or other convenient place. This provides the members of the congregation a chance to socialize with each other and to greet