14 Such is their error, such their pestilent teaching; to support it they borrow the words of Scripture, perverting its meaning and using the ignorance of men as their opportunity of gaining credence for their lies. Yet it is certainly by these same words of God that we must come to understand the things of God. For human feebleness cannot by any strength of its own attain to the knowledge of heavenly things; the faculties which deal with bodily matters can form no notion of the unseen world.
Neither our created bodily substance, nor the reason given by God for the purposes of ordinary life, is capable of ascertaining and pronouncing upon the nature and work of God. Our wits cannot rise to the level of heavenly knowledge, our powers of perception lack the strength to apprehend that limitless might. We must believe God's word concerning Himself, and humbly accept such insight as He vouchsafes to give. We must make our choice between rejecting His witness, as the heathen do, or else believing in Him as He is, and this in the only possible way, by thinking of Him in the aspect in which He presents Himself to us.
Therefore let private judgment cease; let human reason refrain from passing barriers divinely set. In this spirit we eschew all blasphemous and reckless assertion concerning God, and cleave to the very letter of revelation. Each point in our enquiry shall be considered in the light of His instruction, Who is our theme; there shall be no stringing together of isolated phrases whose context is suppressed, to trick and misinform the unpractised listener. The meaning of words shall be ascertained by considering the circumstances under which they were spoken; words must be explained by circumstances not circumstances forced into conformity with words.
We, at any rate, will treat our subject completely; we will state both the circumstances under which words were spoken, and the true purport of the words. Each point shall be considered in orderly sequence.
Source: On the Trinity (New Advent)