A.B. Simpson emphasizes the concept of practical love as outlined in James Chapter 4, contrasting it with sentimental love. He explains that true love is selfless and sacrificial, exemplified by the royal law to love one's neighbor as oneself. Simpson highlights that this law is not only the foundation of the kingdom of God but also the guiding principle for Christian conduct, urging believers to act without partiality and to show mercy. He calls for a love that manifests in practical actions, such as helping those in need and fostering a spirit of gentleness and peace. Ultimately, Simpson encourages Christians to embody this royal law of love in their daily lives, reflecting the love of Christ in all interactions.