John Calvin on James 4:12

12 There is one lawgiver Griesbach adds καὶ κριτής, “and judge,” a reading favored by many MSS. and the versions; and doubtless it makes the passage more complete, especially as what follows belongs to the judge rather than to the lawgiver, that is, to save or to destroy. Now he connects the power of saying and destroying with the office of a lawgiver, he intimates that the whole majesty of God is forcibly assumed by those who claim for themselves the right of making a law; and this is what is done by those who impose as a law on others their own nod or will. And let us remember that the subject here is not civil government, in which the edicts and laws of magistrates have place, but the spiritual government of the soul, in which the word of God alone ought to bear rule. There is then one God, who has consciences subjected by right to his own laws, as he alone has in his own hand the power to save and to destroy.

It hence appears what is to be thought of human precepts, which cast the snare of necessity on consciences. Some indeed would have us to shew modesty, when we call the Pope antichrist, who exercises tyranny over the souls of men, making himself a lawgiver equal to God. But we learn from this passage something far more, even that they are the members of Antichrist, who willingly submit to be thus ensnared, and that they thus renounce Christ, when they connect themselves with a man that is not only a mortal, but who also extols himself against him. It is, I say, a prevaricating obedience, rendered to the devil, when we allow any other than God himself to be a lawgiver to rule our souls.

Who art thou. Some think that they are admonished here to become reprovers of their own vices, in order that they might begin to examine themselves, and that by finding out that they were not purer than others, they might cease to be so severe. I think that their own condition is simply suggested to men, so that they may think how much they are below that dignity which they assumed, as Paul also says, “Who art thou who judgest another?” (Romans 14:4.)

James 4:13-17

13 Go to now, ye that say, To day or to morrow we will go into such a city, and continue there a year, and buy and sell, and get gain:

13 Age nunc, qui dicitis, Hodie et cras eamus in civitatem, et transigamus illic annum unum, et mercemur et lucremur;

14 Whereas ye know not what shall be on the morrow. For what is your life? It is even a vapour, that appeareth for a little time, and then vanisheth away.

14 Qui nescitis quid cras futurum sit; quae enim est vita nostra? vapor est scilicet ad exiguum tempus apparens, deinde evanescens:

15 For that ye ought to say, If the Lord will, we shall live, and do this, or that.

15 Quum dicere debeatis, Si Dominus voluerit, et vixerimus, faciemus hoc vel illud.

16 But now ye rejoice in your boastings: all such rejoicing is evil.

16 Nunc autem gloriamini in superbiis vestris; omnia gloriatio talis, mala est.

17 Therefore to him that knoweth to do good, and doeth it not, to him it is sin.

17 Qui ergo novit facere bonum, nec facit, peccati reus est.