In 70 A.D. the Romans destroyed Jerusalem’s temple along with the whole city and its inhabitants.
But, since the Pharisees had always cooperated with them, the Romans let the Pharisees and their families escape the doomed city, allowing them to settle at the town of Jamnia on the Mediterranean. Encamped there, they heard news of the destruction of their temple, and they began asking what that would mean for them.
The religion of the Pharisees had always centered on temple worship. Loss of the temple left them asking if they still had any core to their religion. Thad had them deciding that what made them Jews was not the temple, but their keeping kosher. Opting for that, they began saying anyone who did not keep kosher was not a Jew.
Up to that time almost all Christians were Jews, abstaining from pork, shrimp, and lobster. But like Jesus, those Christians were ignoring one no-no of orthodox Jews. They were eating with Gentiles who did not keep kosher.
That difference decided the Pharisees on declaring that no one who ate with Gentiles could call himself Jewish. They went on to say that Jesus, by eating with sinner, had set himself to abolishing the law and the prophets.
In today’s Gospel Matthew quoted Jesus as saying, “Do not think I have come to abolish the law and the prophets. No, I have come to fulfill them.”
Moses and the law had gone only half way in saying we should not kill. Jesus fulfilled that law by saying we should not even be angry with others.
Moses and the law said we should not commit adultery. Jesus brought us the rest of the way by saying we should not even lust after others.