In his treatise, "On the Necessity of Reforming the Church," a document to be presented by the leaders of the Protestant movement to the Emperor Charles V, Calvin wrote.
"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."