What Is The Altar Used For In A Church?

What Is The Altar Used For In A Church? altar, in religion, a raised structure or place that is used for sacrifice, worship, or prayer. What is the thing behind the altar? A reredos (/ˈrɪərˌdɒs, ˈrɪərɪ-, ˈrɛrɪ-/ REER-dos, REER-ih-, RERR-ih-) is a large altarpiece, a screen, or decoration placed behind the altar in a church.