Joseph Benson's Commentary of the Old and New Testaments - Exodus 13:9
Exodus 13:9. Upon thy hand, between thine eyes Proverbial expressions, denoting that these things were never to be out of their minds. The Jews, however, understood this literally, and hence the use of phylacteries among them, pieces of parchment inscribed with sentences of their law, which they bound upon their left hand, and placed upon their foreheads between their eyes. read more
Albert Barnes' Notes on the Whole Bible - Exodus 13:9
Hebrew writers have generally regarded this as a formal injunction to write the precepts on slips of parchment, and to fasten them on the wrists and forehead; but other commentators are generally agreed that it is to be understood metaphorically. The words appear to be put into the mouths of the parents. They were to keep all the facts of the Passover constantly in mind, and, referring to a custom prevalent ages before Moses in Egypt, to have them present as though they were inscribed on... read more