A church, "a house of prayer in which the Eucharist is celebrated and reserved, where the faithful assemble, and where is worshipped the presence of the Son of God our Savior, offered for us on the sacrificial altar for the help and consolation of the faithful - this house ought to be in good taste and a worthy place for prayer and sacred ceremonial." In this "house of God" the truth and the harmony of the signs that make it up should show Christ to be present and active in this place.
Source: Catechism of the Catholic Church (Vatican.va)