Complex sentence: Gregory Palamas (1296-1359) was a monk of Mount Athos in Greece and later Archbishop of Thessalonica known as a preeminent theologian and a proponent of hesychasm.
Split into simpler sentences: Gregory Palamas (1296-1359) was a monk of Mount Athos in Greece, and later became Archbishop of Thessalonica. He was a preeminent theologian and a proponent of hesychasm.