Question: Jesus condemned anyone who would say to a brother, Thou fool, and said that such would be in danger of Gehenna fire (Matthew 5: 22), but did He not come under His own condemnation when He called the scribes and Pharisees “fools and blind” (Matthew 23: 17, 19) and when He called His own disciples “fools” (Luke 24: 25)?
Answer: Jesus was speaking about the sixth commandment of the Law in Matthew 5: 21, 22. He showed that malicious anger against a brother is murder in the heart, and that it may be manifested in reviling and in condemnation of a brother as being senselessly wicked and hopeless. But when in Matthew 23: 17, 19 He called the scribes and Pharisees fools, or foolish ones, He had no malicious anger toward them in His heart. In righteous anger He disapproved of their evil deeds and condemned them accordingly, but He did not wish them any evil.
In fact, it was in love that He was laying down His life for them (John 6: 51). They were both foolish and blind, and in love He was telling them this for their own good, not to revile them (1 Peter 2: 23). It is not the use of the word “fool” (moros) itself, but the use of it in the spirit of malicious anger that brings guilt upon the one who does so. A different Greek word (anoetoi) is used in Luke 24: 25. It is translated “fools” in the King James Version, but would better be translated thoughtless ones or inconsiderate ones (see Diaglott).