Not sure whether this will answer any criticisms being lobbed at Christians in this thread or not, as I am seeing several consecutive posts from our sister Phoebe Ann about the councils and the Trinity, which tells me that someone I'm ignoring is probably trying to start some ruckus. Peter1000...or Fatboys...probably Peter...you should know better!
Councils have never existed to invent doctrine, and there is nothing in any of them that you cannot find in the earlier prayers of the Church and the writings of the ante-Nicene Fathers, as I have pointed out with regard to the Holy Trinity many, many times (being present in one form or another in the writings of HH St. Ignatius of Antioch, HH St. Theophilos of Antioch, St. Gregory Thaumaturgus, etc., all of whom were pre-Nicaea). Nicaea was a watershed moment for Christianity because it was the first ecumenical council, i.e., the first gathering involving the whole ecumene (the Greek term for the inhabited world, as it was known at the time), gathering bishops from all around the world where there were Christian churches by that point (with some who were too far afield or otherwise unable to attend in person I suppose probably represented by the churches by whom they were hierarchically administered already, e.g., the long-existing Church of India being represented by the Mesopotamians, or the nascent Axumite Church, depending on when exactly you believe it was founded -- since dates range from just before Nicaea to 330 AD, just after it -- by the Egyptians, who would administer it for approximately 1,600 years). Before that there had been many, many local/regional councils (synods), such as those at Phrygia in the 170s to deal with the Montanists, one in or around Rome in the 140s to deal with Marcion and his followers (not sure where exactly it was held, but Marcion was a rich ship builder in Rome, so it would make sense that he was the local bishop's problem), the by that point many synods of Antioch and those of Carthage, the synod of Elvira in what is now Spain c. 305 AD (notable for being the first appearance in writing of a mandate for clerical celibacy in the Roman Church), etc.
I get the feeling there is an idea among those who are suspicious of the ecumenical councils (you know, the kind of who believe that Constantine "invented" the Biblical canon at Nicaea in 325 and other similar fantasies) that ecumenical councils were all big 'power grabs' for the officials of the government and/or church to corrupt Christianity for money and power and wimmins or something, and...nope. That's simply not the case. The difference between an ecumenical council and a synod is one of scope.
In Orthodox Christianity, anyway, each individual Church in the communion is governed by a Holy Synod comprised of bishops of each territory of the particular Church in question (e.g., in the Coptic Orthodox Church: the bishop of Gharbia, the bishop of Qena, the bishop of Khartoum, etc.), which together form the highest governing authority of the Church. Yes, even higher than the Coptic Orthodox Pope (who is properly also the bishop of Alexandria; in the Orthodoxy, the Pope is a bishop, not some separate office, higher than that of bishop), since the Coptic Pope has the honor of chairing the synod (by virtue of his position as the most senior bishop of the Church), but the synod can depose and/or censure him (and has in the past, when necessary). This is a difference between us and the other famous "Papal" Church, the Roman Catholic Church, which is not Orthodox and for which this set up is the opposite (the Roman Pope cannot be forcibly deposed by a synod of his brother bishops, as a synod is not of higher authority than him, as per the declarations of the first Vatican Council of 1870).
But for the other churches which don't have Popes and are Orthodox, it works much the same: the synod is responsible for meeting to discuss church matters, interpret canons and answer difficult questions regarding how to apply them (note: not all churches necessarily have the same canons or, if they do, they don't necessarily read them in the same way; in Egypt, we share 13 canons in common with the Greeks/Chalcedonians, and have another 100+ that are unique to us, but obviously we do not consult with the Greeks on the interpretation of those 13 shared canons, since we're not in communion with one another anymore, and hence are governed by separate synods with our own traditions), and other things like that.
Looked at properly, then, the council and the synod are actually more like a break or safety valve on the ambitions of people who might otherwise abuse their power (not that this doesn't still happen, people being people and all), since errant presbyters, bishops, and even errant patriarchs know that they will have to answer to either their own synod or (should things get bad enough, e.g., in the case of Nestorius, the one-time Patriarch of Constantinople) an ecumenical council, either of which can and will deal with them accordingly. We of course hope that they would take direction from their immediate superiors long beforehand, in the case of a rogue priest or bishop here or there, but sometimes things can grow out of control for various reasons and then it requires more than meetings between individual leaders to fix the problem.