Outward sacrifice, to be genuine, must be the expression of spiritual sacrifice: "The sacrifice acceptable to God is a broken spirit. . . . " The prophets of the Old Covenant often denounced sacrifices that were not from the heart or not coupled with love of neighbor. Jesus recalls the words of the prophet Hosea: "I desire mercy, and not sacrifice." The only perfect sacrifice is the one that Christ offered on the cross as a total offering to the Father's love and for our salvation. By uniting ourselves with his sacrifice we can make our lives a sacrifice to God.
-- CCC 2100
Art: The Widow's Mite, Gustave Doré, 1866.