Hebrews 5:12-13

For though by this time you ought to be teachers [because of the time you have had to learn these truths], you actually need someone to teach you again the elementary principles of God’s word [from the beginning], and you have come to be continually in need of milk, not solid food. For everyone who lives on milk is [doctrinally inexperienced and] unskilled in the word of righteousness, since he is a spiritual infant.