Don't make a mockery of God. He knows the heart of men and he has proven beyond any doubts. Truth be told, you, me, and all around us are proof. YET he knows men has little faith and so JESUS came to live among MEN, to reveal the glory of God.
Simply put, God in the flesh, came down and live among men to reveal the glory of his kingdom. AND he died for mankind. What more proof does God has to go through to satisfy mankind's lack of faith.
Like in the time of Noah, people either believe a great big flood will be coming and prepares for it or wait until it's upon them to believe.