Nicene and Post-Nicene Fathers, Vol. II:
On Christian Doctrine: Chapter 28

Chapter 28.— It is Safer to Explain a Doubtful Passage by Other Passages of Scripture Than by Reason.

39.  When, however, a meaning is evolved of such a kind that what is doubtful in it cannot be cleared up by indubitable evidence from Scripture, it remains for us to make it clear by the evidence of reason.  But this is a dangerous practice.  For it is far safer to walk by the light of Holy Scripture; so that when we wish to examine the passages that are obscured by metaphorical expressions, we may either obtain a meaning about which there is no controversy, or if a controversy arises, may settle it by the application of testimonies sought out in every portion of the same Scripture.