Complex sentence: Ordained as a Paulist priest in 1899, he served the Church for ten years until, unable to accept its authoritarianism and its prohibition of Modernist thought, he resigned and, while living in Cleveland, became a member of the Unitarian Church.
Split into simpler sentences: Ordained as a Paulist priest in 1899, he served the Church for ten years. He resigned and, while living in Cleveland, became a member of the Unitarian Church.