Hebrews 5:11-14

About this we have much to say which is hard to explain, since you have become dull of hearing. For though by this time you ought to be teachers, you need some one to teach you again the first principles of God's word. You need milk, not solid food; for every one who lives on milk is unskilled in the word of righteousness, for he is a child. But solid food is for the mature, for those who have their faculties trained by practice to distinguish good from evil.