What is the reason God kept Judaism and Christianity separated in the early church?
God deliberately kept Judaism and Christianity apart in the early church so the Gentile mission would not be anchored in Jerusalem or the Twelve. Paul and Barnabas were commissioned and sent from Antioch, not Jerusalem, and returned there. This separation, though the two share beginnings, was God's design.
Les explains that God would not have Paul go back to Jerusalem, learn everything from the twelve, and make Jerusalem the jump-off place into the Gentile world. Instead, Paul and Barnabas were first commissioned by the Holy Spirit at Antioch, about 150–200 miles north of Jerusalem, and sent to the Gentiles in western Turkey. Antioch was where they left from and returned to; later Paul and Silas left from there again and came back. Not Jerusalem. Les says all of this shows God keeping Judaism and Christianity far apart, even though they are connected by their beginnings. Coming back to II Corinthians chapter 5, he notes Paul can write that from henceforth we know no man after the flesh, and though we have known Christ in the flesh, yet henceforth we know Him no more. Les warns that most preaching today comes from Christ's earthly ministry; some of that is proper, for we must understand Bethlehem and the virgin birth, but the separation remains the point.