During worship, it is not only the celebrant who is called to participate fully, but also the gathered people who concelebrate together with him. However, historically it occurred that the professional choir took on itself all the opportunities of the people to that participation, while they became "an audience", almost as if in a theatre. Meanwhile of note is the fact that the Greek χορός, found in service books, means not only "choir" as a group of singers, but also "gathering, multitude", which implies a unified, common invocation of God. Therefore the active participation of all the people in the church during worship "with one voice and one heart" is necessary: with singing and especially common responses ("Amen", "Lord, have mercy", "It is meet and right..." and others).