This is a very important point because we know that the early church received the writings of the various Apostles or their approved disciples AS the Word of God. The Christians received the writings AS from God, himself. It is nonsense to think that God inspired and directed the writings but then just left it up to a group to keep, preserve and determine what came from him. The councils that formalized the canon were not deciding which were Scripture or not. The Scriptures helped to formulate the tradition of faith in the community of believers and that faith tradition helped to shape the canon of Scripture.
Although a number of Christians have thought that church councils determined what books were to be included in the biblical canons, a more accurate reflection of the matter is that the councils recognized or acknowledged those books that had already obtained prominence from usage among the various early Christian communities. (http://www.tektonics.org/lp/ntcanon.html)
Of course, absent a cheap and easy way of printing out the letters and writings, much of the apostolic teachings were committed to memory and were orally transmitted, but the teachings WERE committed to the written word. As time went by and heresies began infiltrating the church, there was more motivation for the church to "canonize" the writings of the Apostles and their disciples.
In a perverse sort of way, heretics were partially responsible for the formation of the NT canon. They motivated the church to identify - and eventually canonize - the true works of the Apostles. These heretical movements, therefore, had a "collective" influence on the setting of the canon.[Gamb.NTC, 65]
That is quite good, except that I would take exception to the identification of 'true works of the Apostles'. We know of many changes during the first 400 years and that some Scripture wasn't written until AD 150 or so. It was what the Church harmonized Scripture into being. Don't forget that the baptismal formula in Matthew was changed to Trinitarian.
Much of what has been definitively defined as doctrine by the Church came about because of heresy. When such heretical beliefs became widespread or threatened orthodoxy, the Church had to move to make a final declaration of Truth.
It has been thus from the very beginning and it is why an authority is necessary to protect orthodoxy.