Answer by Robert Brow
February 2000 (www.brow.on.ca)
I like to think that by word and example Jesus gave his "But I say to you" to clarify the kind of language game that God had in mind for the ten commandments. Patriarchal religion and the Pharisees and Sadducees of his day had added to or misinterpreted what God had said. Jesus corrected their misuse of the language games for murder and adultery (Matthew 5:21-22, 27-28), Sabbath keeping (Mark 2:27-28), parents (Matthew 15:5-6), stealing (Mark 12:40) and covetousness (Matthew 6:25-33).
In relation to the commandment about taking God's name in vain He never suggested it referred to bad language. And in Matthew 23 he clarified the meaning of the third commandment from a string of examples of Pharisee hypocrisy.
In any case "God did not send the Son into the world to condemn the
world, but in order that the world might be saved through Him" (John
3:17). And the real problem with human sin is not bad language but
that "Light has come into the world and people loved darkness rather than
light because their deeds were evil" (John 3:19). Which suggests
that our job is not to produce conviction of sin by nit picking about human
wrongness, but go for the jugular as Paul did, and "open their eyes so
that they may turn from darkness light and from the power of Satan to God"