Hebrews 5:11-14

11About this we have much to say, and it is hard to explain, since you have become dull of hearing. 12For though by this time you ought to be teachers, you need someone to teach you again the basic principles of the oracles of God. You need milk, not solid food, 13for everyone who lives on milk is unskilled in the word of righteousness, since he is a child. 14But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.