It may sound odd to say, but not all orthodox statements are true. Some are false!
This is obvious if we think about it. For there are some issues on which the Church has not yet infallibly taught. And about those issues theologians debate. If two theologians have contradictory views on a matter the Church has not definitively settled, then each opinion is “orthodox,” yet both opinions cannot be true.
Take the dispute that existed before the Church defined Mary’s Immaculate Conception. The Thomists (followers of St. Thomas Aquinas’s method and principles) argued that Mary could not have been immaculately conceived, since if she were she would not have needed t be redeemed by Christ. But on all counts, she was redeemed by Christ. The Scotists (followers of Duns Scotus’s method and principles) argued that Mary was redeemed in the most perfect way, by being immaculately conceived. In fact, the Thomists were wrong. However, before the Church infallibly pronounced on the topic (mid 19th century), the Church respected the Thomists with the difficulties they perceived regarding this issue. Thus, the Thomists were not condemned; they were “orthodox” but wrong.
These observations have important ramifications for the present. Many people think that if a theologian is “orthodox” that all is well with his views. This is not necessarily the case. Some orthodox opinions are false.
What, then is orthodoxy? Well, the Church teaches both positively and negatively; she affirms some truths and rejects some errors. Hence, it would be helpful to consider orthodoxy under two aspects. The first aspect is giving the requisite assent to Magisterial teachings according to their proper level of authority. We could call this positive orthodoxy. The second aspect is rejecting those errors condemned by the Magisterium according to the level of authority with which the condemnations are issued. We could call this negative orthodoxy. So, the full meaning of orthodoxy is both positive and negative.
Now, orthodoxy thus described is a necessary condition for Catholic theology. Theology is a reflection on the faith by the faith. Thus, theology presupposes faith. Since faith comes from above and is the acceptance of the revelation which God commends to the Church, the theological project cannot get off the ground unless all these starting points – the Church, revelation, faith – are presupposed / set in place.
Nevertheless, orthodoxy is by no means a sufficient condition for good theology. Even a fully orthodox theologian might not be a good theologian. What is needed is sound method, prayerful contemplation, solid principles, learning in the Tradition, philosophical acumen, accurate argumentation, and fruitful analogical insight.