The Law was added because of transgressions.
Jesus ministered while the Law was still in effect.
"Even so we, when we were children, were in bondage under the elements of the world. 4 But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, 5 to redeem those who were under the law, that we might receive the adoption as sons."
Even though Jesus operated in a different economy than the Law, He was still bound, as a man, to the Law's statutes. Now, the wages of sin is death. Yet, Jesus had no sin and still death took Him. This was a violation of the limit of death. Therefore, God the Father raised Him to life, demonstrating that even death has no power over Christ. This is how He disarmed the principalities publicly and triumphed over them.
15 Having disarmed principalities and powers, He made a public spectacle of them, triumphing over them in it.
Now, in covenant principles, the covenant remains in effect as long as the man is alive. Once he is dead, the covenant no longer has jurisdiction over the life of the man.
When Jesus died, he did so for the benefit of all men: He took on the the rightful punishment for the sins of men even though He had no sin Himself:
"..but now, once at the end of the ages, He has appeared to put away sin by the sacrifice of Himself."
It was His death that put an end to the power and curse of the Law. However, He didn't just die Himself, He died for the sins of men. Therefore, the jurisdiction of the covenant of Law ended not just for Jesus but for all men who would likewise identify in His death.
"And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together with Him, having forgiven you all trespasses, 14 having wiped out the handwriting of requirements that was against us, which was contrary to us. And He has taken it out of the way, having nailed it to the cross."
The life given by the Father to Christ is also promised to all who identify in Him: a life not under the curse of the Law but an eternal life in God.
Paul began his preaching from this point. Paul knew, even as a Jew, that the Law no longer directed his steps, the Spirit of God did. And this Spirit was available to Paul because he identified himself in the One who overcame death and sin: Christ.