What was the Canaanite woman's most costly mistake?
Her most costly mistake was addressing Jesus as 'thou son of David.' That was a Jewish term, and she was a Gentile. She had no right to presume upon the covenants given to Israel. Later she dropped that title and called Him 'Lord,' which brought her closer.
Les explains that the woman was a Gentile, and the disciples urged Jesus to send her away because she was a nuisance. Jesus said He was not sent but to the lost sheep of the house of Israel, because the covenants were Jew only, with no Gentiles included. So she was presuming on something she had no right to. Her most costly mistake was in verse 22, when she addressed Him as 'thou son of David.' That was a Jewish term and qualified who He was and where she was coming from. A Gentile could not address Him that way. When she came back in verse 25, she dropped the 'son of David' part and addressed Him as 'Lord,' which brought her a little closer. She then said, 'Lord, help me.' Jesus answered that it was not meet to take the children's bread and cast it to dogs. The children are the Jews; the dogs are the Gentiles. Les illustrates with his own house dog waiting for crumbs, showing the analogy: you cannot take what belonged to Israel and give it to a Gentile. But she persisted, saying the dogs eat the crumbs that fall from their master's table.
And, behold, a woman of Canaan came out of the same coasts, and cried unto him, saying, Have mercy on me, O Lord, thou son of David; my daughter is grievously vexed with a devil.