Isaiah 28:9-10 English Standard Version
9 “To whom will he teach knowledge, and to whom will he explain the message? Those who are weaned from the milk, those taken from the breast?
10 For it is precept upon precept, precept upon precept, line upon line, line upon line, here a little, there a little.”
A precept is a command or an ordinance, that which is given to obey. Ref. BLB.ORG
Psalm 119:56 English Standard Version (ESV) This blessing has fallen to me, that I have kept your precepts.
A concept is an abstract idea; a general notion. Source MW Dictionary
A precept that is not understood properly, nor taught properly, loses the attachment of the blessing that comes with obeying the precept in truth. Verse 9 was included with the opening passages for one reason. Knowledge comes to those who have been weaned from the milk of the word, the gospel.
Hebrews 5:12-14 English Standard Version
12 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.
Hebrews 6:1 English Standard Version (ESV) Therefore let us leave the elementary doctrine of Christ and go on to maturity, not laying again a foundation of repentance from dead works and of faith toward God,
We are not meant to be babes in Christ forever. We are meant to grow in Christ and over time develop sufficient understanding of the precepts of God not only to obey them, but share the truth of the blessings that come from understanding those precepts.
Why should the lost receive the gospel if they cannot see the blessings that come from believing and obeying?