15 We who are Jews by birth and not Gentile “sinners” -Galatians 2:15 BSB
A person born in a Jewish family had a high probability of knowing and worshiping the true God, Yahweh—the Creator of heaven and earth.
6 These words I am commanding you today are to be upon your hearts. 7 And you shall teach them diligently to your children and speak of them when you sit at home and when you walk along the road, when you lie down and when you get up. 8 Tie them as reminders on your hands and bind them on your foreheads. 9 Write them on the doorposts of your houses and on your gates. -Deuteronomy 6:6-9 BSB
Gentiles, on the other hand, had a tremendous disadvantage compared to Jews because almost all of them were born into pagan families who worshiped false deities. That’s why Gentiles were called, in those times, sinners.
Paganism is the worship of idols and demons and also participating in offering their children up to their false gods in sacrificial rituals. Paganism is another way to say witchcraft. The practice of paganism continues to this day with modern terms like abortion, to give one example.