Catechism of the Council of Trent for Parish Priests

The Necessity of Religious Instruction

Such is the nature of the human mind and intellect that, although by means of diligent and laborious inquiry it has of itself investigated and discovered many other things pertaining to a knowledge of divine truths; yet guided by its natural lights it never could have known or perceived most of those things by which is attained eternal salvation, the principal end of man’s creation and formation to the image and likeness of God.

It is true that the invisible things of God from the creation of the world are, as the Apostle teaches, clearly seen, being understood by the things that are made: his eternal power also, and divinity But the mystery which hath been hidden from ages and generations so far transcends the reach of man’s understanding, that were it not made manifest by God to His Saints, to whom He willed to make known by the gift of faith, the riches of the glory of this mystery among the Gentiles, which is Christ, man could by no effort attain to such wisdom.