In Matthew 15:24, Jesus said “I was sent only to the lost sheep of Israel”, (during his initial refusal to help a Canaanite woman)

Earlier in Matthew 10, Jesus instructed the disciples… “Do not go among the Gentiles or enter any town of the Samaritans, Go rather to the lost sheep of Israel”

Its clear that Jesus was addressing only the Israelites and not even the Gentiles and Samaritans living among them. His purpose did not include everybody, or he would have instructed his disciples to preach to the gentiles and samaritans.

Jesus did not even have anything to do with the non-Israelites during his life on earth…
So on what basis do christians believe that “Jesus died for the sins of all mankind”?

NOTE : “Israel” in this context is clearly the biblical Israel, i.e genetically connected to the Abraham. So please dont redefine Israel to fit your beliefs. “Christians are the new Israel” etc.