A series of excellent one-page leaflets explaining vital aspects of the Catholic Faith is available here (pdf). One of them, entitled Why go to Mass?, has this to say:
'Put together all our good actions, all the social work of NGOs, all the sacrifices of martyrs and saints, and they are just specks of dust compared with the infinite value of Jesus’ sacrifice made present in the Mass. “All good works in the world are the works of men. But the Mass is the work of God.” (St. John Mary Vianney)'
Background information on their spread around the world can be read here. Click image for pdf.