In Hebrews 5:12-14

“For 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, 13 for everyone who lives on milk is unskilled in the word of righteousness, since he is a child. 14 But solid food is for the mature, for those who have their powers of discernment trained by constant practice to distinguish good from evil.”