A Visible Reminder to Obey
Most commentators connect this verse with Numbers 15:38, explaining that the fringes (or tassels) on the four corners of the outer garment were a constant, physical reminder for the Israelites to remember and obey all of God's commandments. Charles Ellicott adds that they may have also served as a memorial for the man executed for Sabbath-breaking, reinforcing the seriousness of obedience.