Complex sentence: He was born into an aristocratic famly and educated in the Priory of Saint-Martin-des-Champs at Paris, became a Benedictine, and in 1150 was made Abbot of La Celle near Troyes, whence his surname, Cellensis.
Split into simpler sentences: He was born into an aristocratic famly and educated in the Priory of Saint-Martin-des-Champs at Paris. He became a Benedictine, and in 1150 was made Abbot of La Celle near Troyes, where he got his surname, Cellensis.