Complex sentence: His first ministry was as Assistant Curate at St Mary Abbots, Kensington, although within 5 years he was Vicar of St Matthew's, Northampton--a post he held from 1937 to 1955.
Split into simpler sentences: His first ministry was as assistant curate of St Mary Abbots, Kensington. Within five years he was vicar of St Matthew's Northampton, a position he held from 1937 to 1955.