Dehonianer
Baaij was born in Rotterdam into a non-Catholic home. He was introduced to the Catholic faith as a young man, and immediately felt called to become a priest. His parents allowed him to take catechism classes and to be received into the Catholic Church. Still feeling a draw to the ministry, he explored entering the minor seminary of the local diocese, but found that the tuition was beyond his family's means. By chance, he encountered a member of the Congregation of the Priests of the Sacred Heart and entered their seminary. He persevered and was ordained a priest on 20 July 1947.