Complex sentence: The Roman Catholic Church, the Eastern Orthodox Church and Oriental Orthodoxy permit married men to become clergymen (with certain limitations), but do not permit clergy to marry after ordination.
Split into simpler sentences: The Roman Catholic Church, the Eastern Orthodox Church and Oriental Orthodoxy may have married clergy, but do not admit clerical marriage. With certain limitations, they permit married men to become clergymen, but do not permit clergy to marry after ordination.