What is Christian doctrine?
It is “What the church of Jesus Christ believes, teaches, and confesses on the basis of the word of God”.
Jaroslav Pelikan, Credo, p. xii
“Underlying the creedal and conciliar definition of orthodoxy from the beginning have been three shared presuppositions: first that there is a straight line...from the Gospels to the creed; consequently, second, that the true doctrine being confessed by the councils and creeds of the church is identical with what the NT calls 'the faith which was once for all delivered to the saints'; and therefore, third, that continuity with that faith is the essence of orthodoxy, and discontinuity with it the essence of heresy”.
Jaroslav Pelikan, Credo, p. 9