Deuteronomy 6:8

And thou shalt bind them for a sign upon thine hand, as a reminder that they should be performed at all times; and they shall be as frontlets between thine eyes, as a reminder that the words of the Lord should be the chief object of meditation in the believer. The Jews, in later times, insisted upon a literal understanding of the command, and it became the fashion among the more devout Jews to wear little cases with the Scripture-texts Exodus 13:1; Exodus 11-17; Deuteronomy 6:4; Deuteronomy 11:13, called Tephillim, fastened to the left hand and to the forehead-the phylacteries of Matthew 23:5.