Arnold Janssen was born on November 5, 1837 in Goch, a small city in lower Rhineland (Germany). The second of ten children, his parents instilled in him a deep devotion to religion. He was ordained a priest on August 15, 1861 for the diocese of Muenster and was assigned to teach natural sciences and mathematics in a secondary school in Bocholt. There he was known for being a strict but just teacher. Due to his profound devotion to the Sacred Heart of Jesus, he was named Diocesan Director for the Apostleship of Prayer. This apostolate encouraged Arnold to open himself to Christians of other denominations.