James 4:12

There is one lawgiver
The Alexandrian copy, and others, and the Syriac, Ethiopic, and Vulgate Latin versions, add, "and judge". Who is the one only Lord God, ( Isaiah 33:22 ) . This is a character that may be applied to God the Father, who gave the law to the people of Israel, both the judicial and ceremonial law, and also the moral law; from his right hand went a fiery law, and to him belongs the giving of it; and also to the Son of God, the Lord Jesus who is King of saints, and lawgiver in his house; who has given out commandments to be observed, and laws of discipline for the right ordering of his house, and kingdom, to be regarded; and particularly the new commandment of love, which is eminently called the law of Christ; and which is most apparently broke, by detraction and speaking evil one of another: now there may be inferior and subordinate lawgivers, as Judah is said to be God's lawgiver, and Moses is said to command the Jews a law; yet there is but one supreme, universal, and perfect lawgiver, who is God; and though there may be many lawgivers in things political, whose legislative power is to be obeyed, both for the Lord's sake, and for conscience sake; yet in things religious, and relating to conscience, God is the only lawgiver, who is to be hearkened unto:

who is able to save,
and to destroy; this is true of God the Father, who is able to save, and does save by his Son Jesus Christ, and even persons that have broken the law he has given, and are liable to the curse and condemnation of it; and he is able to save them according to that law, in perfect consistence with it, and with his justice and holiness, since Christ, by whom he saves, was made under it, and has fulfilled it; and that Christ is mighty to save, able to save to the uttermost, is certain from the Scripture, and all experience; and God, the lawgiver, is able to destroy both body and soul in hell, for the transgressions of his law; and even Christ the Lamb is also the lion of the tribe of Judah, who will break his enemies in pieces, as a potter's vessel, and punish the contemners of his Gospel with everlasting destruction, from his presence and glory: in a word, God, the lawgiver, is sovereign, and can destroy, or save, whom he pleases; he is able to save the brother that is spoken against, and to destroy him that speaks against him:

who art thou that judgest another?
another man's servant, as in ( Romans 14:4 ) or "thy neighbour", as the Syriac and Ethiopic versions read; or "the neighbour", as the Alexandrian copy, and the Vulgate Latin version; that is, any brother, friend, or neighbour, in the manner as before observed in the preceding verse.