Cf. Vatican Council, Sess. 2, cap. 2: "Though it is due to divine revelation that truths of God, in themselves not inaccessible to human reason, in the present condition of mankind can be known by all readily, with firm certitude, and without admixture of error; still not on that account is revelation to be called absolutely necessary, but because God in His infinite goodness has destined man to a supernatural end, that is, to a share in the good things of God, which altogether surpass the intelligence of the human mind." Faith is the indispensable prelude to the beatific vision, the supernatural end of man. Both are immediate knowledges of God, faith the hearing of His word on earth, vision the seeing of His face in heaven. Without revelation there would be some natural knowledge of God, but not the knowledge of faith.
Of God and His Creatures: 1.5