2 It must therefore belong to Jesus Christ's grace itself to grant both to us to speak without deficiency, and to you to hear with discretion; for discretion is needful not to them only who speak, but also to them that hear, lest they hear one thing, and misconceive another in their mind. Let us then speak concerning the Holy Ghost nothing but what is written; and whatsoever is not written, let us not busy ourselves about it. The Holy Ghost Himself spoke the Scriptures; He has also spoken concerning Himself as much as He pleased, or as much as we could receive. Let us therefore speak those things which He has said; for whatsoever He has not said, we dare not say.
Source: Catechetical Lectures (New Advent)