James wants the person who condemns a brother to remember his place. He has just said that judging a brother is like sitting in judgment over God's law (James 4:11). Now he sets two facts side by side: there is "one lawgiver, who is able to save and to destroy," and there is you. Gill calls Him "but one supreme, universal, and perfect lawgiver, who is God." Barnes says that only He can bind the conscience, and that a frail and erring person should not step in to pronounce judgment on another. The question is short because the answer is obvious.

The answer lies in the first half of the verse: there is only "one lawgiver, who is able to save and to destroy" (James 4:12). The one judging is not that lawgiver. James then turns to those who say, "To day or to morrow we will go into such a city" without thought of God (James 4:13).

"Lawgiver" is the one who makes the law; Barnes says there is "but one who has a right to give law." Barnes stresses that "no laws are binding on the conscience, but those which Christ has ordained." "Able to save and to destroy" speaks of power over life and eternal destiny. Barnes compares Jesus' words, "fear him which is able to destroy both soul and body in hell" (Matthew 10:28), and Paul's question, "Who art thou that judgest another man's servant?" (Romans 14:4).

This question shows that judgment belongs to God because He alone has both the right and the power. He gave the law, and He alone can save or destroy. That truth humbles us and frees us. We are not responsible to be the final judge of our brothers and sisters.

James places this question right after "Humble yourselves in the sight of the Lord" (James 4:10). Speaking evil of a brother takes a seat that is not ours; Barnes warns that "we should not usurp his prerogatives." Matthew Henry's Concise Commentary warns us not to "set up our own notions and opinions as a rule to those about us."