1 A sound mind, and one which does not expose its possessor to danger, and is devoted to piety and the love of truth, will eagerly meditate upon those things which God has placed within the power of mankind, and has subjected to our knowledge, and will make advancement in [acquaintance with] them, rendering the knowledge of them easy to him by means of daily study. These things are such as fall [plainly] under our observation, and are clearly and unambiguously in express terms set forth in the Sacred Scriptures. And therefore the parables ought not to be adapted to ambiguous expressions. For, if this be not done, both he who explains them will do so without danger, and the parables will receive a like interpretation from all, and the body of truth remains entire, with a harmonious adaptation of its members, and without any collision [of its several parts]. But to apply expressions which are not clear or evident to interpretations of the parables, such as every one discovers for himself as inclination leads him, [is absurd.] For in this way no one will possess the rule of truth; but in accordance with the number of persons who explain the parables will be found the various systems of truth, in mutual opposition to each other, and setting forth antagonistic doctrines, like the questions current among the Gentile philosophers.
2. According to this course of procedure, therefore, man would always be inquiring but never finding, because he has rejected the very method of discovery. And when the Bridegroom comes, he who has his lamp untrimmed, and not burning with the brightness of a steady light, is classed among those who obscure the interpretations of the parables, forsaking Him who by His plain announcements freely imparts gifts to all who come to Him, and is excluded from His marriage-chamber. Since, therefore, the entire Scriptures, the prophets, and the Gospels, can be clearly, unambiguously, and harmoniously understood by all, although all do not believe them; and since they proclaim that one only God, to the exclusion of all others, formed all things by His word, whether visible or invisible, heavenly or earthly, in the water or under the earth, as I have shown from the very words of Scripture; and since the very system of creation to which we belong testifies, by what falls under our notice, that one Being made and governs it—those persons will seem truly foolish who blind their eyes to such a clear demonstration, and will not behold the light of the announcement [made to them]; but they put fetters upon themselves, and every one of them imagines, by means of their obscure interpretations of the parables, that he has found out a God of his own. For that there is nothing whatever openly, expressly, and without controversy said in any part of Scripture respecting the Father conceived of by those who hold a contrary opinion, they themselves testify, when they maintain that the Saviour privately taught these same things not to all, but to certain only of His disciples who could comprehend them, and who understood what was intended by Him through means of arguments, enigmas, and parables. They come, [in fine,] to this, that they maintain there is one Being who is proclaimed as God, and another as Father, He who is set forth as such through means of parables and enigmas.
3. But since parables admit of many interpretations, what lover of truth will not acknowledge, that for them to assert God is to be searched out from these, while they desert what is certain, indubitable, and true, is the part of men who eagerly throw themselves into danger, and act as if destitute of reason? And is not such a course of conduct not to build one's house upon a rock which is firm, strong, and placed in an open position, but upon the shifting sand? Hence the overthrow of such a building is a matter of ease.
Source: Adversus haereses (New Advent)