The altar is the special place in which the Mass is celebrated. Think of it as a "table" with a cloth, candles and the food. Our "food" is the Holy Eucharist. This is the body of Jesus as was written in the Bible at the Last Supper. The Catholics received this body of Jesus as a way of being in full communion with the Lord, and being one with Him. Since the body of the Lord sits on the altar, the altar itself is considered a Holy object.
