Charles Ellicott Commentary Deuteronomy 6:8

"And thou shalt bind them for a sign upon thy hand, and they shall be for frontlets between thine eyes." — Deuteronomy 6:8 (ASV)

And thou shalt bind them ... —From this precept the Jews derive the use of the Tephillin, the portions of the Law which they bind upon the head or arm when about to pray.