When God decides to move, it really causes waves. The expansion of the Kingdom from the Jews to the Gentiles wasn't done by writing big words in the sky, but through people. How would you have done it if you were God? It seems that entrusting that kind of news into human hands is an unusual way to do something big, but that is the whole point of Jesus. God wished to fully include his people in His plan, however inefficient it may seem to us.