Albert Barnes Commentary James 2:8

"Howbeit if ye fulfil the royal law, according to the scripture, Thou shalt love thy neighbor as thyself, ye do well:" — James 2:8 (ASV)

If ye fulfil the royal law. This refers to the law he immediately mentions, which requires us to love our neighbor as ourselves.

It is called a "royal law," or kingly law, because of its excellence or nobility. This designation is not because it is ordained by God as a king, but because it holds a prominence and importance among other laws similar to that of a king among other people; in other words, it is majestic, noble, and worthy of veneration.

It is a law that ought to govern and direct us in all our dealings with others—just as a king rules his subjects.

According to the Scripture, Thou shalt love thy neighbour as thyself (Leviticus 19:18). See it explained by the Savior in the parable of the good Samaritan (Luke 10:25–37). Regarding its meaning, refer to the comments on Matthew 19:19.

Ye do well. That is, "if you fairly comply with the spirit of this law, you do all that is required of you in regulating your dealings with others. You are to regard all persons as your neighbors, and are to treat them according to their real worth; you are not to be influenced in judging them, or in your treatment of them, by their clothing, or their complexion, or the circumstances of their birth, but by the fact that they are fellow-beings." This is another reason why they should not show partiality in their treatment of others, for if, in the true sense, they regarded all others as "neighbors," they would treat no one with neglect or contempt.