Complex sentence: Wongwang returned to Silla in 600 and promulgated the Mahayana form of Buddhism, and did so by teaching the faith to the people free of complex jargon and using common words.
Split into simpler sentences: Wongwang returned to Silla in 600 and promulgated the Mahayana form of Buddhism. His method was to teach the faith to the common people free of complex jargon and employing common words.