Providentissimus Deus §15

¹⁵ But he must not on that account consider that it is forbidden, when just cause exists, to push inquiry and exposition beyond what the Fathers have done; provided he carefully observes the rule so wisely laid down by St. Augustine-not to depart from the literal and obvious sense, except only where reason makes it untenable or necessity requires;(40) a rule to which it is the more necessary to adhere strictly in these times, when the thirst for novelty and unrestrained freedom of thought make the danger of error most real and proximate. Neither should those passages be neglected which the Fathers have understood in an allegorical or figurative sense, more especially when such interpretation is justified by the literal, and when it rests on the authority of many. For this method of interpretation has been received by the Church from the Apostles, and has been approved by her own practice, as the holy Liturgy attests; although it is true that the holy Fathers did not thereby pretend directly to demonstrate dogmas of faith, but used it as a means of promoting virtue and piety, such as, by their own experience, they knew to be most valuable. The authority of other Catholic interpreters is not so great; but the study of Scripture has always continued to advance in the Church, and, therefore, these commentaries also have their own honourable place, and are serviceable in many ways for the refutation of assailants and the explanation of difficulties. But it is most unbecoming to pass by, in ignorance or contempt, the excellent work which Catholics have left in abundance, and to have recourse to the works of non-Catholics - and to seek in them, to the detriment of sound doctrine and often to the peril of faith, the explanation of passages on which Catholics long ago have successfully employed their talent and their labour. For although the studies of non-Catholics, used with prudence, may sometimes be of use to the Catholic student, he should, nevertheless, bear well in mind-as the Fathers also teach in numerous passages(41) - that the sense of Holy Scripture can nowhere be found incorrupt outside of the Church, and cannot be expected to be found in writers who, being without the true faith, only gnaw the bark of the Sacred Scripture, and never attain its pith.