Why did they argue over homoousios?
The Arian controversy in the fourth century was arguably the greatest theological controversy in the history of the church. As Protestants, we might think that the Reformation controversies of the sixteenth century were the most momentous. Without wishing to minimize their importance, however, the Arian controversy was greater, because it went deeper. The Reformers were arguing about how we receive the benefits of Christ; the men of the fourth century were arguing about something even more basic—who Christ is. Unless the right foundation is laid in the person of the Redeemer, little is gained in disputing about His benefits. The Arian controversy was sparked, not by Arius himself, but by the outstanding Christian thinker of the previous century, Origen (185–254). Origen had fought vigorously and successfully against one of the gravest threats to the orthodoxy of the third century—Modalism (or “Sabellianism”, after one of its leading advocates). Modalism tried to solve the mystery ...