Heresies Always Start Small
The Council of Nicea teaches that God the Son exists as one substance (homoousian) with God the Father, even though they are different persons of the Blessed Trinity. The word homoousian is Greek for consubstantial in Latin (which you say or sing every Sunday or Feast day at Holy Mass during the Creed.) To deny the persons of the Trinity being consubstantial is to deny both the Divinity of Christ and the Blessed Trinity. This fact of orthodox Catholicism seems obvious to most Catholics today who have taken even one week of Christology classes at a Catholic University or seminary. But in the fourth century, the heretic Arius denied this, [...]