Hypothetically speaking, Yeshua would only reject Christianity if the message of Paul was a complete fabrication.
The teachings Yeshua, if you take the Gospels as valid, were not meant for the Gentiles but only the lost tribes of Israel. Yeshua never rejected the Jewish laws, all 613 of them.
These twelve Jesus sent out with the following instructions: “Do not go among the Gentiles or enter any town of the Samaritans. Go rather to the lost sheep of Israel. (Matthew 10: 5-6)
A Canaanite woman from that vicinity came to him, crying out, “Lord, Son of David, have mercy on me! My daughter is demon-possessed and suffering terribly.” Jesus did not answer a word. So his disciples came to him and urged him, “Send her away, for she keeps crying out after us.” He answered, “I was sent only to the lost sheep of Israel.” The woman came and knelt before him. “Lord, help me!” she said.
He replied, “It is not right to take the children’s bread and toss it to the dogs.”
“Yes it is, Lord,” she said. “Even the dogs eat the crumbs that fall from their master’s table.”
Then Jesus said to her, “Woman, you have great faith! Your request is granted.” And her daughter was healed at that moment. (Matthew 15: 22-28)