*"They" are Calvin's detractors in 16th century France. This quote is taken from the Prefatory Address to King Francis from the Institutes of the Christian Religion.*
Then, again, it is to no purpose they call us to the bar of custom. To make everything yield to custom would be to do the greatest injustice.
Were the judgments of mankind correct, custom would be regulated by the good. But it is often far otherwise in point of fact; for, whatever the many are seen to do, forthwith obtains the force of custom. But human affairs have scarcely ever been so happily constituted as that the better course pleased the greater number.
Hence, the private vices of the multitude have generally resulted in public error, or rather that common consent in vice which these worthy men would have to be law. Any one with eyes may perceive that it is not one flood of evils which has deluged us; that many fatal plagues have invaded the globe; that all things rush headlong; so that either the affairs of men must be altogether despaired of, or we must not only resist, but boldly attack prevailing evils. The cure is prevented by no other cause than the length of time during which we have been accustomed to the disease. But be it so that public error must have a place in human society, still, in the kingdom of God, we must look and listen only to his eternal truth, against which no series of years, no custom, no conspiracy, can plead prescription. Thus Isaiah formerly taught the people of God, "Say ye not, A confederacy, to all to whom this people shall say, A confederacy;" i.e. do not unite with the people in an impious consent;
Isaiah 8:12 "Neither fear ye their fear, nor be afraid. Sanctify the Lord of hosts himself; and let him be your fear, and let him be your dread."
Now, therefore, let them, if they will, object to us both past ages and present examples; if we sanctify the Lord of hosts, we shall not be greatly afraid. Though many ages should have consented to like ungodliness, He is strong who taketh vengeance to the third and fourth generation; or the whole world should league together in the same iniquity. He taught experimentally what the end is of those who sin with the multitude, when He destroyed the whole human race with a flood, saving Noah with his little family, who, by putting his faith in Him alone, "condemned the world" (Heb. 11:7).
In short, depraved custom is just a kind of general pestilence in which men perish not the less that they fall in a crowd. It were well, moreover, to ponder the observation of Cyprian, that those who sin in ignorance, though they cannot be entirely exculpated, seem, however, to be, in some sense, excusable; whereas those who obstinately reject the truth, when presented to them by the kindness of God, have no defence to offer.