Back in the day, particularly for the Israelites, the Law was everything. The law was their standard, their crutch, their security, their hope. Why a curse? Because no one could follow every jot & tittle of the law, and for this reason, they participated in the rituals of sacrifice and atonement. That was the point. The Messiah was promised to be the ultimate reconciliation.
And all who depend on the Law [who are seeking to be justified by obedience to the Law of rituals] are under a curse and doomed to disappointment and destruction, for it is written in the Scriptures, Cursed (accursed, devoted to destruction, doomed to eternal punishment) be everyone who does not continue to abide (live and remain) by all the precepts and commands written in the Book of the Law and to practice them. [Amplified]
This was the proposed road for the Israelites. For them to accept Jesus as the Messiah, they had to accept one final sacrifice as efficacious and complete. To accept the Messiah and then go back to the old way, was restoring the power of the curse.
The second leap for the Jews who accepted Jesus as the Messiah was to accredit the blessings of Abraham (once relegated to their people alone) to the Gentile believers. The exclusive club was no longer a matter of birthright, history, or ancestry.
A single act reboot the system.
As a believer, I am confessing that the work of Christ is the restoration act between me and God. Where the door was closed, it is now open. I may enter the realm of God, the divine. I may participate in holiness. I am permitted to be in relationship . . . not because of what I have done (or not done) but because of who “He” is, that is, the Christ/Messiah for the world.