Hebrews 5:11-14

11 About him we have many words to say, and hard to interpret, seeing you have become dull of hearing.  12 For when by reason of the time you ought to be teachers, you again need to have someone teach you the rudiments of the first principles of the oracles of God. You have come to need milk, and not solid food.  13 For everyone who lives on milk is not experienced in the word of righteousness, for he is a baby.  14 But solid food is for those who are full grown, who by reason of use have their senses exercised to discern good and evil.