During these centuries of incessant struggle great changes supervened in the character and constitution of the two Churches.
In the West the theocratic element became predominant; the Church, left to its own resources, learned to suffice for itself. It gave, instead of asking, protection, grasped the sceptre of absent emperors, and successfully established its dominion over king and princes.
In the East the Church, shielded from harm by the State, remained subservient to civil authority, rarely interfered in political affairs, and was content with its own spiritual jurisdiction.
The persistent pretensions of Rome, the constant antagonism, the frequent wars, the incessant conflicts to which they gave rise, were accompanied by differences of dogma and of discipline. These served to further embitter the struggle, to render the contest more implacable, and to make reconciliation or harmony impossible.
Disputes arose in the second and third centuries as to the date and celebration of Easter. The heresy of Arius, at first, and for a time, accepted in the East, but condemned in the West, followed in the fourth century. In the seventh, discussion as to the double or single nature of Christ convulsed the Christian world. The monotheletian patriarchs and the dyotheletian popes mutually anathematized each other, until unity was restored by the Sixth Œcumenical Council, a.d. 680 to 691. Then came the great controversy on the subject of image worship, which raged with intense virulence for a century and a half.
Meanwhile another grave subject of dispute arose, which still constitutes the essential dogmatical difference between the Churches. The doctrine of the Double Procession of the Holy Ghost originated in Spain during
