Is that exactly what Jesus said? Did Jesus actually say he was the only one who gets it right? If that is the case and he argued for Jewish law and beliefs then wouldn't Christians want to become Jewish?
First of all, the temporary Constitution of the Mosaic Law was only for one nation, the nation of 'ancient' Israel.
Jesus fulfilled the Law (Romans 10:4), so since Pentecost his followers are: Christians.
Jesus first went to the Jews to become his Christian followers - Luke 4:43
Then, at Pentecost, the way was opened up for the Samaritans.
And then, the people of the gentile nations were offered Christianity.