ISB ~ Matthew 5 v22

You fool!:The Greek transliterates an Aramaic term that implies a lack of intelligence. It is an insult that means something like “empty head” or “numskull”.

the hell of fire:The Greek expression (also in 5:29-30) denotes the Valley of Gehenna south of Jerusalem. It served as a large dump where garbage was burned continually. Jesus uses the image to illustrate the frightful reality of damnation (CCC 1034-35).

See word study:Hell at Mk 9.