Then the superstitions observance of Lent had everywhere prevailed: for both the vulgar imagined that they thereby perform some excellent service to God, and pastors commended it as a holy imitation of Christ; though it is plain that Christ did not fast to set an example to others, but, by thus commencing the preaching of the gospel, meant to prove that his doctrine was not of men, but had come from heaven. And it is strange how men of acute judgment could fall into this gross delusion, which so many clear reasons refute: for Christ did not fast repeatedly (which he must have done had he meant to lay down a law for an anniversary fast), but once only, when preparing for the promulgation of the gospel. Nor does he fast after the manner of men, as he would have done had he meant to invite men to imitation; he rather gives an example, by which he may raise all to admire rather than study to imitate him. In short, the nature of his fast is not different from that which Moses observed when he received the law at the hand of the Lord (Exodus 24:18; 34:14:28). For, seeing that that miracle was performed in Moses to establish the law, it behoved not to be omitted in Christ, lest the gospel should seem inferior to the law. But from that day, it never occurred to any one, under pretense of imitating Moses, to set up a similar form of fast among the Israelites. Nor did any of the holy prophets and fathers follow it, though they had inclination and zeal enough for all pious exercises; for though it is said of Elijah that he passed forty days without meat and drink (1 Kings:19:8), this was merely in order that the people might recognise that he was raised up to maintain the law, from which almost the whole of Israel had revolted. It was therefore merely false zeal, replete with superstition, which set up a fast under the title and pretext of imitating Christ; although there was then a strange diversity in the mode of the fast, as is related by Cassiodorus in the ninth book of the History of Socrates: “The Romans,” says he, “had only three weeks, but their last was continuous, except on the Lord’s day and the Sabbath. The Greeks and Illvrians had, some as, others seven, but the f’ast was at intervals. Nor did they differ less in the kind of food: some used only bread and water, others added vegetables; others had no objection to fish and fowls; others made no difference in their food.” Augustine also makes mention of this difference in his latter epistle to Januarius.
Calvin, Institutes 4.12.20