The direction of the early church was determined by the Apostles who actually knew Christ, followed by giants such as Paul, who were responsible for the rapid spread of Christianity in the latter part of the 1st century, especially to the Greeks (non Jews).
But, after the disciples and Paul had died the leadership and direction of the church was past on to those who had studied under the apostles and had been blessed by the Holy Spirit. Some of those became giants of the church themselves and took the Christian faith on the new lands and through them, the faith spread to even greater numbers. Some stayed in the main centres of the early church, in Jerusalem, Alexandria, Rome, Smirna and so on. Many of them undertook their work under extreme persecution from the Romans and Jews and many were martyred for their steadfast faith in Jesus Christ.
We owe a great debt of gratitude to those early church fathers who kept the faith alive in difficult times, until it was adopted by Rome as the 'official faith' when the persecution finally subsided and Christians could live in relative peace and security and the faith could grow organically.
Those earliest Church Fathers are usually referred to as Ante-Nicene Fathers meaning, before the Council of Nicaea in 325 AD