17 Have thou ever in your mind this seal, which for the present has been lightly touched in my discourse, by way of summary, but shall be stated, should the Lord permit, to the best of my power with the proof from the Scriptures. For concerning the divine and holy mysteries of the Faith, not even a casual statement must be delivered without the Holy Scriptures; nor must we be drawn aside by mere plausibility and artifices of speech. Even to me, who tell you these things, give not absolute credence, unless thou receive the proof of the things which I announce from the Divine Scriptures. For this salvation which we believe depends not on ingenious reasoning, but on demonstration of the Holy Scriptures.
Of the Soul.
Source: Catechetical Lectures (New Advent)