Jesus declares that his words ought to define our lives. Not because this makes life better but because his words are life and rejection of his words are death and destruction.
By whose authority does Jesus speak these words? His own.
So is Jesus a megalomaniac, melonhead or the master of life? Is he liar, lunatic or lord?
This is quite a finish to the Sermon on the Mount and shapes all that has come before. Come and explore Jesus' words and his authority.