John Gill Commentary Proverbs 4:21

"Let them not depart from thine eyes; Keep them in the midst of thy heart." — Proverbs 4:21 (ASV)

Let them not depart from your eyes
Commit them to writing, frequently read them over; let them be always in sight, as a rule and directory to steer the course of life by. Some understand this of the wicked, as if the sense was, let not them, the wicked, cause them to depart from your eyes; nor you to neglect them, by their bad advice, solicitations to sin, and ill examples; (See Gill on Proverbs 3:21); keep them in the midst of your heart ;
lay them up there, and ponder them; often meditate upon them, and do not forget them; show the most affectionate regard unto them, and look upon them as a most inestimable treasure, for which no place so fit a repository as the heart.