Charles Ellicott Commentary Numbers 15:39

"and it shall be unto you for a fringe, that ye may look upon it, and remember all the commandments of Jehovah, and do them; and that ye follow not after your own heart and your own eyes, after which ye use to play the harlot;" — Numbers 15:39 (ASV)

That ye seek not after your own heart.—Or, That you go not about, or search not out, etc.