If it be inquired then by what things chiefly the Christian religion has a standing existence among 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 by 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 an din due form, or otherwise, is to bring them to this test. If any one is desirous of a clearer and more familiar illustration, I would say, that regimen in the Church, the pastoral office, and all other matters of order, resemble the body, whereas the doctrine which regulates the due worship of God, and points out the ground on which the consciences of men must rest their hope of salvation, is the soul which animates the body, renders it lively and active, and, in short, makes it not to be a dead and useless carcass.

John Calvin, The Necessity of Reforming the Church, 13-14.