Complex sentence: In 1651, John Eliot established Natick and Ponkapoag as praying towns, communities of natives who had converted to Christianity and were willing to live a in a more traditional "English" lifestyle, i.e. permanent agricultural settlements.
Split into simpler sentences: In 1651, John Eliot established Natick and Ponkapoag as praying towns. They were reserved for Native Americans who had converted to Christianity and were willing to live according to English custom in permanent agricultural settlements.