There is one lawgiver, who is able to save and to destroy: who art thou that judgest another? There is one lawgiver - Και κριτης, And judge, is added here by AB, about thirty others, with both the Syriac, Erpen's Arabic, the Coptic, Armenian, Ethiopic, Slavonic, Vulgate, two copies of the Itala, Cyril of Antioch, Euthalius, Theophylact, and Cassiodorus. On this evidence Griesbach has received it into the text.
The man who breaks the law, and teaches others so to do, thus in effect set himself up as a lawgiver and judge. But there is only one such lawgiver and judge - God Almighty, who is able to save all those who obey him, and able to destroy all those who trample under feet his testimonies.
Who art thou that judgest another? - Who art thou who darest to usurp the office and prerogative of the supreme Judge? But what is that law of which St. James speaks? and who is this lawgiver and judge? Most critics think that the law mentioned here is the same as that which he elsewhere calls the royal law and the law of liberty, thereby meaning the Gospel; and that Christ is the person who is called the lawgiver and judge. This, however, is not clear to me. I believe James means the Jewish law; and by the lawgiver and judge, God Almighty, as acknowledged by the Jewish people. I find, or think I find, from the closest examination of this epistle, but few references to Jesus Christ or his Gospel. His Jewish creed, forms, and maxims, this writer keeps constantly in view; and it is proper he should, considering the persons to whom he wrote. Some of them were, doubtless, Christians; some of them certainly no Christians; and some of them half Christians and half Jews. The two latter descriptions are those most frequently addressed.