Jerome
Catena Aurea · Matthäusevangelium 5
For I say unto you, That except your righteousness shall exceed the righteousness of the Scribes and Pharisees, ye shall in no case enter into the kingdom of heaven. Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment: But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
Or, Racha is a Hebrew word signifying, ‘empty,’ ‘vain;’ as we might say in the common phrase of reproach, ‘empty-pate.’ Observe that He says brother; for who is our brother, but he who has the same Father as ourselves?