Complex sentence: They held a Christmas Love Feast at Harriseahead, with many standing on or between the pews, which began a time of revival when many Primitive Methodist leaders, most importantly William Clowes, were converted.
Split into simpler sentences: They held a Christmas Love Feast at Harriseahead, with many standing on or between the pews. This began the time of revival when some key Primitive Methodist leaders, most importantly William Clowes, were converted.