- Affirmation of Holy Tradition
- Recognition of the authority of the seven Ecumenical Councils
- Return to the original form of the Nicene Creed (without the filioque clause inserted at the Council of Toledo, 589 A.D.)
- Recognition of all seven Sacraments
- Rejection of 'the heresies of the Reformation' and subsequent 'isms' that resulted when Protestants rejected the authority of Holy Tradition: Calvinism, anti-sacramentalism, iconoclasm, Gnosticism, and the feminism and the egalitarianism that led to the ordination of women priests and the consecration of women as bishops.
David Bentley Hart’s comments on Calvinism (published in an interview in Christian Century) are helpful in understanding why Orthodoxy regards much of Calvin’s thought as heretical. Here is an excerpt from the interview:
CC: Followers of Calvin have been particularly concerned to defend God's sovereignty. Do you think that tradition presents a particular problem for Christian thinking today?
DBH: Yes--and not only today. I quite explicitly admit in my writing that I think the traditional Calvinist understanding of divine sovereignty to be deeply defective, and destructively so. One cannot, as with Luther, trace out a direct genealogy from late medieval voluntarism to the Calvinist understanding of divine freedom; nevertheless, the way in which Calvin himself describes divine sovereignty is profoundly modern: it frequently seems to require an element of pure arbitrariness, of pure spontaneity, and this alone separates it from more traditional (and I would say more coherent) understandings of freedom, whether divine or human.
This idea of a God who can be called omnipotent only if his will is the direct efficient cause of every aspect of created reality immediately makes all the inept cavils of the village atheist seem profound: one still should not ask if God could create a stone he could not lift, perhaps, but one might legitimately ask if a God of infinite voluntaristic sovereignty and power could create a creature free to resist the divine will. The question is no cruder than the conception of God it is meant to mock, and the paradox thus produced merely reflects the deficiencies of that conception.
Frankly, any understanding of divine sovereignty so unsubtle that it requires the theologian to assert (as Calvin did) that God foreordained the fall of humanity so that his glory might be revealed in the predestined damnation of the derelict is obviously problematic, and probably far more blasphemous than anything represented by the heresies that the ancient ecumenical councils confronted." -- David Bentley Hart
John Calvin was trained as a lawyer and a humanist. He was not a theologian who knew Holy Tradition and his writings were of a polemical nature, set to do battle with Roman Catholicism. Calvin admits that his wisdom has nothing to do with the Holy Tradition received from the Apostles. He wrote:
Our wisdom, in so far as it ought to be deemed true and solid Wisdom, consists almost entirely of two parts: the knowledge of God and of ourselves. But as these are connected together by many ties, it is not easy to determine which of the two precedes and gives birth to the other. For, in the first place, no one can survey himself without forthwith turning his thoughts towards the God in whom he lives and moves; because it is perfectly obvious, that the endowments which we possess cannot possibly be from ourselves; nay, that our very being is nothing else than subsistence in God alone. In the second place, those blessings which unceasingly distil to us from heaven, are like streams conducting us to the fountain. ... Every person, therefore, on coming to the knowledge of himself, is not only urged to seek God, but is also led as by the hand to find him. -- John Calvin, Institutes of the Christian Religion, Book 1, Chapter 1, Paragraph 1
Orthodoxy holds that knowledge of God cannot be had apart from Holy Tradition. This is the error of Protestants as a whole and one which has given ground to many ideologies opposed to Holy Tradition and Scripture.
To read more on Calvin's views, go here.