John Calvin: Mere Christianity

"If it be inquired then by what things chiefly the Christian religion has a standing existence amongst us, and maintains its truth, it will be found that the following two not only occupy the principal place, but comprehend under them all the other parts , and consequently the whole substance of Christianity, viz., a knowledge, first, of the mode in which God is duly worshipped; and, secondly, of the source from which salvation is to be obtained. When these are kept out of view, though we may glory in the name of Christians, our profession is empty and vain. After these come the Sacraments and the Government of the Church, which as they were instituted for the preservation of these branches of doctrine, ought not to be employed for any other purpose and, indeed, the only means of ascertaining whether they are administered purely and in due form, or otherwise, is to bring them to this test" (John Calvin, The Necessity of Reforming the Church, 13-14).