Heb 5:11 Concerning him we have much to say, and it is hard to explain, since you have become dull of hearing.
Heb 5:12 For though by this time you ought to be teachers, you have need again for someone to teach you the elementary principles of the oracles of God, and you have come to need milk and not solid food.
Heb 5:13 For everyone who partakes only of milk is not accustomed to the word of righteousness, for he is an infant.
Heb 5:14 But solid food is for the mature, who because of practice have their senses trained to discern good and evil.
The elementary teachings of:
repentance from dead works
Heb 4:2 For indeed we have had good news preached to us, just as they also; but the word they heard did not profit them, because it was not united by faith in those who heard.