Christians should obey (literally fulfill) the royal law, just as Jesus fulfilled the law by coming and teaching ((Matthew 5:17; 22:34–40).
It is the royal law because it belongs to the kingdom and our glorious Lord (King) gave it (James 2:5).
in Scripture: James shifts from a general mention of the law to a specific commandment from “the holiness code” (Leviticus 19). It explains how we show our love for God through relationships with others (see Leviticus 19:18; Deuteronomy 6:5).
Love your neighbor as yourself: This quote from Leviticus 19:18 means treating your neighbor as you would treat yourself.