Ephesians 3:9. “And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, Who created all things by Jesus Christ:”
I think, in order for us to understand what a huge job God had given to Paul, we would need to go back through the ages into the mind of Judaism as it existed in the Old Testament. They knew that God had made them the people of the promise. What promise? That through them, the Messiah would come; all the nations of the earth would be blessed; that they would multiply like the sand on the seashore, the stars in the sky. To them was given the Old Testament Law. They were God’s peculiar (special, set aside, chosen) people, and they were keenly aware of that status.
Then Jesus came, and they didn’t recognize Him. After His death and resurrection, many Jews finally did see the truth. Persecution arose, and they dispersed into the surrounding nations. Paul visited wherever God directed him, and always found a reception among believing Jews who, it would seem, had been sharing their new faith with their Gentile neighbors. Still, the majority of the known world at that time had never heard of Jesus Christ, and Paul was tasked with changing all that.