This verse connects 5:20–48 as a single unit (see study note on Matthew 4:23–25).
be perfect: The word “perfect” means maturity, wholeness, and full devotion to God. It describes a complete response to the message of Jesus about the kingdom (19:21; Ephesians 4:13; Philippians 3:15; Colossians 1:28; 4:12; 1 John 4:18). True perfection has love at its center (see Luke 6:36).