[Holy Scripture]… is not sufficient to guide man to salvation, inasmuch as, firstly, it wasn’t given to man from the beginning and, secondly, when it was given it wasn’t the only authentic text, with regard to the salvation of human souls, because before it there was the Holy Tradition. Many years before Moses began writing the first books of the Old Testament, there was sacred piety in the community of the people of Israel. Similarly, the books of the New Testament began to be written ten years after the formal foundation of the Church, which took place on the day of Pentecost. The Church chose and sealed as inspired by God the books of the two Testaments over one hundred years later.  These then comprised the declared Canon of the books of Holy Scripture. Thereafter the Church maintained this Canon of Truth, inasmuch as it is the very pillar and ground of truth (1 Tim. 3:15). The Holy Spirit operates within all of this for the preservation of the truth about salvation. Where the Church is, says Saint Jerome, there also is the Spirit of God and where the Spirit of God is, there also is the Church and all grace – since the Spirit is truth.”
– ‘The Truth of Our Faith’ Part 2