Hebrews 5:13

"For every one that partaketh of milk is unskilled in the word of righteousness: for he is a babe." What is "the Word of righteousness"? He seems to me here to hint at conduct also. That which Christ also said, "Except your righteousness shall exceed the righteousness of the Scribes and Pharisees", this he says likewise, "unskilled in the word of righteousness," that is, he that is unskilled in the philosophy that is above, is unable to embrace a perfect and exact life. Or else by "righteousness" he here means Christ, and the high doctrine concerning Him. That they then were "become dull," he said; but from what cause, he did not add, leaving it to themselves to know it, and not wishing to make his discourse hard to bear. But in the case of the Galatians he both "marveled" and "stood in doubt", which tends much more to encourage, as it is the language of one who would never have expected that this should happen. For this is what the doubting implies. Thou seest that there is another infancy, Thou seest that there is another full age. Let us become of "full age" in this sense: It is in the power even of those who are children, and the young to come to that "full age": for it is not of nature, but of virtue.