Orthodox and Catholics: what is the difference?

The Orthodox nuance

First, honestly, what Catholics say. For them, the bishop of Rome, the pope, has authority over the whole Church, a universal governance, and, under certain conditions, he can state a teaching without error. For a Catholic, the unity of the Church holds around the pope.

Orthodoxy says something else, and not out of pride. Yes, in the first millennium Rome had a place of honour, a primacy, but among brother bishops, not above them as a master. Truth in the Church is not guarded by one single man, but by the whole Church together, and it is stated in councils, where the bishops gather and the Holy Spirit confirms. No single bishop, not even the one of Rome, can change or add anything to the faith of all on his own. That is the heart of the disagreement, more than any quotation thrown from one side or the other.

And this is seen best in the Filioque. The Creed said that the Holy Spirit proceeds from the Father, as Christ Himself says (John 15, 26). The West added and from the Son. The problem, for the Orthodox, is not only what was added, but above all how: a change to the common Creed of the whole Church, made without an ecumenical council, by one side alone. The Creed belongs to no one to rewrite by himself.

The rest, what you often hear, purgatory, the Immaculate Conception, unleavened bread, are real differences, but they flow from the same root as above: the way we understand authority in the Church.