What does Matthew 15:24 mean?

Throughout His earthly ministry, Jesus acted with a crystal-clear sense of His purpose. Eventually, all nations of earth would be blessed through Israel, in the person of Jesus, as the Son of God gave His life as the sacrifice for the sins of humanity. For that to happen, however, Jesus needs to accomplish certain things within the people of Israel. So, for now, Jesus has come to serve and heal God's chosen people as the promised Messiah. Only after His own people officially reject Him will the offer be made for all to come into the family of God through faith in Christ (John 1:11–12).

Jesus uses the same language with her as when He sent disciples out in pairs to the towns and villages of Galilee (Matthew 10:5–6). He strictly forbids them from going into the Gentile territories. They are only to take the message of the kingdom to the lost sheep of the house of Israel. This is the same reason given here for refusing—for now—to cast the demon from the daughter of this Canaanite woman begging Him for help. He has not been sent by His Father to heal the Gentiles, yet.