For the word is used by our Paul in writing to the Corinthians, who were Greeks, and not yet purified in their morals: “I have fed you with milk, not with meat; for hitherto you were not able to bear it, neither yet now are you able, for you are yet carnal: for whereas there is among you envying and strife, are you not carnal, and walk as men?” Now the same writer, knowing that there was a certain kind of nourishment better adapted for the soul, and that the food of those young persons who were admitted was compared to milk, continues: “And you have become such as have need of milk, and not of strong meat.
For every one that uses milk is unskilful in the word of righteousness; for he is a babe. But strong meat belongs to them that are of full age, even those who by reason of use have their senses exercised to discern both good and evil.” Would then those who believe these words to be well spoken, suppose that the noble doctrines of our faith would never be mentioned in an assembly of wise men, but that wherever (our instructors) see young men, and a mob of slaves, and a collection of foolish individuals, they bring publicly forward divine and venerable truths, and before such persons make a display of themselves in treating of them?
But it is clear to him who examines the whole spirit of our writings, that Celsus is animated with a hatred against the human race resembling that of the ignorant populace, and gives utterance to these falsehoods without examination.
Source: Against Celsus (New Advent)