Jamieson, Fausset & Brown, on Jas 4:12

“There is one lawgiver, and judge, that is able to destroy and to deliver.”

“There is one lawgiver--The best authorities read in addition, "and judge." Translate, "There is One (alone) who is (at once) Lawgiver and Judge, (namely) He who is able to save and destroy." Implying, God alone is Lawgiver and therefore Judge, since it is He alone who can execute His judgments; our inability in this respect shows our presumption in trying to act as judges, as though we were God. who art thou, &c.--The order in the Greek is emphatic, "But (inserted in oldest manuscripts) thou, who art thou that judgest another?" How rashly arrogant in judging thy fellows, and wresting from God the office which belongs to Him over thee and THEM alike! another--The oldest authorities read, "thy neighbor."”

Imported from an open dataset — not yet checked against the printed edition.