Deuteronomy 6:8

thou shalt bind them for a sign … for frontlets, etc.] See for the exact meanings the notes on Exodus 13:9; Exodus 13:16. As there, so here probably the injunction is to be taken metaphorically and not literally, as the later Jews understood it, though they carried it out not by tattooing, which seems the meaning here, but by writing these words as well as Deuteronomy 11:15-21 and Exodus 13:1-16 on small parchment rolls, enclosing them in metal covers, and wearing them, bound on the arm and brow, at morning prayer. They are called in late Hebrew tephillinand in the N.T. φυλακτἡρια. See E.B.-Frontlets."