The law of the prophets was a costly covenant between old-testament god and humanity. Or, you know, whatever subgroup was in charge of translations at the time.
The “fulfillment” mentioned is a single lump sum of holy lamb blood in place of the never-actually-complete exchange of not wearing blended fabrics, not getting tattoos, and sacrificing your firstborn on a rock in the mountains. And slaughtering prisoners of war who you tricked into getting circumcised as a condition of their surrender so that they would be vulnerable.