Complex sentence: When the ball disappeared over a very high wall, he knew he must try to climb over and he awoke with the firm conviction that was never to leave him: that he must follow that light, Bahá'u'lláh, forevermore.
Split into simpler sentences: When the ball disappeared over a very high wall, he knew he must try to climb over it. He awoke with the firm conviction that was never to leave him: that he must follow that light, Bahá'u'lláh, forevermore.