All seven ecumenical councils, between 325 and 787 ad, essentially dealt with the Person of Jesus Christ. Even the seventh, which had to do with whether the use of icons is idolatry (it isn't), comes down to what one believes about Jesus. He has adorned the earth with beauty not only in his creation of it, but ultimately in his joining of himself to mankind in his own Person. This is at the heart of the whole Christian faith, and it is critical for us to know it. Here's the podcast.
The Sixth council, in Constantinople, ad 680, affirmed that Christ has not one, but two wills: divine and human; this is an affirmation of his true humanity, including the will. Otherwise, his redemption of man is in question. The seventh council, in Nicaea, ad 787, affirmed the veneration of icons and images as helpful aids to worship of Christ. This is in itself an affirmation of his incarnation, his adornment of the earth with his union with human flesh. St. Paul's on the Air podcast.
Political considerations (a desire to unify the empire against invasions) entered into the proceedings of the Second Council of Constantinople in ad 553, never a good idea. A desire to mollify both sides led to agreements that were church-wide, but the Monophysites (who believed that Christ had only one nature, a mixture of divine and human and therefore fully neither) were not really handled head-on, and therefore much less was accomplished than should have been. Confessions of faith must be clear, and we must ever seek to know well who Jesus is: true God, true man, and therefore our Redeemer and Lord. St. Paul's on the Air for Sunday, June 16th.
In ad 451 the bishops from all over Christendom met in Chalcedon, in the largest of the seven ecumenical councils to affirm the two natures of Christ--that he is fully human and fully divine--in one Person, against Eutyches, who was saying that Christ had only one nature, a mixture of divine and human. The error is deadly, for it holds that Christ is neither human nor divine, in which case our salvation is lost, for he cannot redeem us (mankind), and he has not the capacity, as God, to do so. The podcast is here.