Good people do not need law. Paul says;
“realizing the fact that law is not made for a righteous person, but for those who are lawless and rebellious, for the ungodly and sinners, for the unholy and profane, for those who kill their fathers or mothers, for murderers and immoral men and homosexuals and kidnappers and liars and perjurers, and whatever else is contrary to sound teaching,” 1 Timothy 1:9–10 (NASB95)
And it could not save. It forced wicked people to act good under threat of death, exile, war, sickness, poverty and the like. While promising physical temporary benefits for obedience. The obedient thought they were good for not stealing when they wanted to. But good people do not want to steal.
Abraham and all believers did not need the law, but naturally fulfilled it through the Two Great Commandments of love for God and people written on their hearts.
After the wicked served their purpose, God removed them from Israel leaving only the faithful like Abraham under Christ. He did this by abolishing the Law (Jeremiah 31:31–33) and replacing it with the New Covenant for believers only. To this Israel, God grafts in believing gentiles. And any of the broken off ethnic Israel who come to faith in Christ.