An explanation

Here is how we see it.  Jesus taught his disciples everything they needed to know about a faithful life and eternity.  The disciples, becoming apostles, passed this life/doctrine on to their successors, ad infinitum. The Holy Spirit, as promised by Jesus, led and is leading his church in faithfulness.  This means that there has never been a time when the church was not.
This is not to say that the church has not had bad bishops or gone through difficult times.  But that is how things are improved and clarified.   The seven ecumenical councils were held in response to heretical assaults from within and outside of the church.  In essence, the council's were not about introducing new doctrine but were about clarifying what the church had always believed and practiced.
This is why we believe that the Eastern Orthodox Church is "the" church.  God formed it, gave it its mission and has provided direction by the power of the Holy Spirit, from the very beginning.