1 The God of all Providence, Who in the adorable designs of His love at first elevated the human race to the participation of the Divine nature, and afterwards delivered it from universal guilt and ruin, restoring it to its primitive dignity, has in consequence bestowed upon man a splendid gift and safeguard - making known to him, by supernatural means, the hidden mysteries of His Divinity, His wisdom and His mercy. For although in Divine revelation there are contained some things which are not beyond the reach of unassisted reason, and which are made the objects of such revelation in order "that all may come to know them with facility, certainty, and safety from error, yet not on this account can supernatural Revelation be said to be absolutely necessary; it is only necessary because God has ordinated man to a supernatural end."(1) This supernatural revelation, according to the belief of the universal Church, is contained both in unwritten Tradition, and in written Books, which are therefore called sacred and canonical because, "being written under the inspiration of the Holy Ghost, they have God for their author and as such have been delivered to the Church."(2) This belief has been perpetually held and professed by the Church in regard to the Books of both Testaments; and there are well-known documents of the gravest kind, coming down to us from the earliest times, which proclaim that God, Who spoke first by the Prophets, then by His own mouth, and lastly by the Apostles, composed also the Canonical Scriptures,(3) and that these are His own oracles and words(4) - a Letter, written by our heavenly Father, and transmitted by the sacred writers to the human race in its pilgrimage so far from its heavenly country.(5) If, then, such and so great is the excellence and the dignity of the Scriptures, that God Himself has composed them, and that they treat of God's marvellous mysteries, counsels and works, it follows that the branch of sacred Theology which is concerned with the defence and elucidation of these divine Books must be excellent and useful in the highest degree.
Source: Providentissimus Deus (Vatican.va)