Now, after understanding this illustration, we have to apply it to the qualities of spiritual food with which the rational part of man is nourished. See, then, if Plato and the wise men among the Greeks, in the beautiful things they say, are not like those physicians who confine their attentions to what are called the better classes of society, and despise the multitude; whereas the prophets among the Jews, and the disciples of Jesus, who despise mere elegances of style, and what is called in Scripture “the wisdom of men,” “the wisdom according to the flesh,” which delights in what is obscure, resemble those who study to provide the most wholesome food for the largest number of persons.
For this purpose they adapt their language and style to the capacities of the common people, and avoid whatever would seem foreign to them, lest by the introduction of strange forms of expression they should produce a distaste for their teaching. Indeed, if the true use of spiritual food, to keep up the figure, is to produce in him who partakes of it the virtues of patience and gentleness, must that discourse not be better prepared when it produces patience and gentleness in multitudes, or makes them grow in these virtues, than that which confines its effects to a select few, supposing that it does really make them gentle and patient?
If a Greek wished by wholesome instruction to benefit people who understood only Egyptian or Syriac, the first thing that he would do would be to learn their language; and he would rather pass for a Barbarian among the Greeks, by speaking as the Egyptians or Syrians, in order to be useful to them, than always remain Greek, and be without the means of helping them. In the same way the divine nature, having the purpose of instructing not only those who are reputed to be learned in the literature of Greece, but also the rest of mankind, accommodated itself to the capacities of the simple multitudes whom it addressed.
It seeks to win the attention of the more ignorant by the use of language which is familiar to them, so that they may easily be induced, after their first introduction, to strive after an acquaintance with the deeper truths which lie hidden in Scripture. For even the ordinary reader of Scripture may see that it contains many things which are too deep to be apprehended at first; but these are understood by such as devote themselves to a careful study of the divine word, and they become plain to them in proportion to the pains and zeal which they expend upon its investigation.
Source: Against Celsus (New Advent)