What was the purpose of the Law, and how were Old Testament believers saved? The Law points to our need for grace before a holy God, and the foundation of salvation has always been Christ.
Wherever Paul went on his missionary journeys, God raised up other Christians to assist him. In Acts 18, we see this ecclesiastical synergy at work again.
On his missionary journeys, Paul encountered many kinds of people. He had to be able to relate to them all in order to spread the good news of Jesus Christ.