Complex sentence: In 1815, at the age of 12, he joined the Congregation of the Virgin Mary and the monastic order of the Antonins "Lebanese Maronite Order" three years later, vowing chastity, poverty, and obedience.
Split into simpler sentences: In 1815, at the young age of 12, he joined the Congregation of the Virgin Mary. Three years later, at the age of 15, he joined the monastic order of the Antonins "Lebanese Maronite Order", vowing chastity, poverty, and obedience.