“Just as people were guided in the knowledge of God and on the path of salvation by Holy Tradition alone (that is, by a living voice—oral tradition) during the period of time before the books of the Old Testament were written, so were the people similarly guided before books of the New Testament were written. Holy Tradition was the guide by which the first Christians were directed to the path of salvation. The first Person to bring the teachings of the New Testament with a living voice to the ears of the people was our Saviour Jesus Christ Himself, Who taught the people continually for three and a half years, spreading His Gospel without writing any of it down. Inasmuch as He was fulfilling His obedience to His Father, He did not send His Apostles to write the Gospel, but rather to preach it to the whole world, saying: Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit: Teaching them to observe all things whatsoever I have commanded you: and lo, I am with you always, even unto the end of the world. Amen (Mat. 28:19-20). From its establishment in (33 AD) until the year 44 AD, when the Holy Apostle Matthew wrote the first Gospel,[1] the Church was governed without the Scriptures of the New Testament, but by Holy Tradition, only part of which was later recorded. Although there were many other writers who were considered inspired and faithful scribes of the Apostles, it is the Church which did or did not recognize them, for She is unerring. The Church lived the truth of the Gospel even before anything was committed to writing, having lived by Holy Tradition from the outset.
 
Thus, Holy Tradition is this: the source and the root of the two Testaments—the Old and the New—and this is why we call it a source of Holy Revelation, for it carries the same weight as Holy Scripture.”
~ ‘The Truth of Our Faith’