Complex sentence: For 28 years, from his initial conversion until his debility from Parkinson's disease, Jenner engaged in this form of evangelism, probably speaking with more than 100,000 people in total, hundreds of whom made initial professions of conversion to Christianity.
Split into simpler sentences: For 28 years, from his initial conversion until his debility from Parkinson's disease, Jenner engaged in this form of evangelism. He probably spoke with more than 100,000 people in total, hundreds of whom made initial professions of conversion to Christianity.