Even you agree the law has changed, right? Hebrews 7:12
So, why are heaven and earth still here, since you claim that Jesus is saying no change can occur before heaven and earth pass away?
Observance of the Law changed from the Christian perspective. We do not observe the letter of the Law but rather the law was fulfilled through Christ and our covenant is through Christ.
Why are heaven and earth still here?
That is where the debate is.
Ezekiel has a lot to say about the future temple....a place where God will dwell forever....sacrifices continue.
And then you get into the whole Red Heifer thing.
Some see that the Old Covenant is no longer in effect.
Some see that the Old Covenant still pertains for the Jews.
Now you look at the struggles that Paul had with the Judaizers, he was not saying that the Jewish religion was not valid. He was saying that the Mosaic Law did not pertain to Christians. If you wanted to convert to Judaism, one the first things you did was to be circumcised. Paul was saying that was not necessary for Christians....and if you did then you had to follow the whole law...and effectively you were severed from Christ.
To understand this you have to realize that there was two different Christian sects in the biblical era. The Jewish-Christians and the Gentile-Christians. You take James for example, what we know of him is that he still observed the Sabbath on Saturday and there is a debate if he was still sacrificing.
James was either Christ's step brother or half brother through his mother. He cannot be his brother because Joseph was not his father.....he was not one of the twelve....and we do not know how he came to be the leader of the Apostles....out of Jerusalem. Either way the conflict between Paul and the judaizers was the reason for the meeting in Jerusalem. At that meeting there is no discussion that the Jewish religion was no longer valid, just that the Christian did not have to observe the 613 Mosaic Laws and Jewish customs.
So if the Mosaic Law still continued for Jewish-Christians and Jews then it could last until heaven and earth pass away and all things fulfilled. Certainly Christ fulfilled the law....but is that all that is going to be fulfilled?