Hebrews 5:12-6:3 (New International Version)

¹²In fact, though by this time you ought to be teachers, you need someone to teach you the elementary truths of God's word all over again. You need milk, not solid food! ¹³Anyone who lives on milk, being still an infant, is not acquainted with the teaching about righteousness. ¹⁴But solid food is for the mature, who by constant use have trained themselves to distinguish good from evil.

Hebrews 6

 ¹Therefore let us leave the elementary teachings about Christ and go on to maturity, not laying again the foundation of repentance from acts that lead to death,^[a] and of faith in God, ²instruction about baptisms, the laying on of hands, the resurrection of the dead, and eternal judgment. ³And God permitting, we will do so.