God did not give his system of government by law and judges to the early church. The early Christians were not in a position to implement an alternative system of government, so they would have becomes embroiled in unnecessary conflict with Rome and distracted from the gospel.
Instead gave his system of laws much earlier, so that it would be available for the church when needed. The perfect time to give the law was when the Israelites were entering the promised land. They needed laws at that time to organise their society to maintain peace. The benefit of God’s law is that it worked reasonably well without the gospel, so it was OK to give it to his people before the gospel. Then it would be there for the early church when it needed.
Of course, God’s system of justice will work much better with the gospel.