hmm did Jesus lie to Paul?
"you are not under law, but grace"
The 'letter of the OT demanded 'instant punishment (stoning) and this is what Paul ref to when he said we are not under it anymore but now have received GRACE/pardon from that, pardon from immediate death in the form of Grace to give us time to be changed from our previous Disobedience to NOW become obedient.
THAT is the 'change in the law...Not that the law itself had to be changed or abolished !!! To fulfill the law one has to LEARN to obey and keep it....we can not remain children of DISobedience !!! Heb 5v8,9.
The fault is with MAN...Not the law.