“The Rabbis spoke from authority, Jesus with authority. Those who heard Him ‘were astonished at his teaching, for he taught them as one that had authority, and not as the scribes’ (Mark 1:22. C. H. Dodd renders ‘He taught them like a sovereign, and not like the Rabbis’). W. Manson . . . cites the saying of Justin Martyr, ‘His word was power from God.’ ‘Thus says the Lord’ is typical of the Old Testament, but Jesus’ characteristic expression is ‘Truly, truly, I say to you.’ The difference is significant. Jesus appealed to no other authority as He spoke to men of the deep things of God.”
Leon Morris, The Lord from Heaven (Downers Grove, 1974), pages 13-14. Italics his.