48 Nay, the wiser of the Hebrews tell us that there was of old among the Hebrews a most excellent and praiseworthy law, that every age was not entrusted with the whole of Scripture, inasmuch as this would not be the more profitable course, since the whole of it is not at once intelligible to everyone, and its more recondite parts would, by their apparent meaning, do a very great injury to most people. Some portions therefore, whose exterior is unexceptionable, are from the first permitted and common to all; while others are only entrusted to those who have attained their twenty-fifth year, viz., such as hide their mystical beauty under a mean-looking cloak, to be the reward of diligence and an illustrious life; flashing forth and presenting itself only to those whose mind has been purified, on the ground that this age alone can be superior to the body, and properly rise from the letter to the spirit.
Source: Orations (New Advent)