Quick answer
Bring your heart, not just your ears, to what wisdom teaches. The verse is a hinge in the Thirty Sayings: a fresh call to receive, placed between warnings, because none of the warnings work on a heart that has not been applied.
Read both lines
The two lines assign a task to two organs. The ears get the easier job, positioning themselves where words of knowledge are spoken. The heart gets the real one: "apply" is the language of bringing something to the instruction and pressing it there, the way you apply weight or apply a seal. Hearing wisdom is passive and constant; applying the heart is deliberate and rare. The sages knew the difference between a student in the room and a student in the lesson.
Placed here, between the saying about the exploiter's Redeemer and the saying about correcting a child, the verse works as a re-invitation. The Thirty Sayings pause periodically to ask for the hearer's heart again (22:17 opened the whole collection the same way), because instruction only transfers where attention has been given, not merely granted.
Related: Proverbs 22:17 · Proverbs 2:1–5 · Proverbs 4:20–22
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.