A leather box containing four sections of the law (Ex 11:13-21) written on parchment, and which Jewish men tied to the forehead and left arm (close to the heart) before morning prayers. The practice of wearing phylacteries arose, probably after the exile, from a literal interpretation by pious Jews of passages such as Ex 13:9.
The significance of wearing phylacteries
A reminder of God’s requirements Dt 11:13-21 Phylacteries, when worn, were to be an outward sign of the importance of taking God’s word into the heart; Ps 119:11; Pr 3:1-3 See also Dt 6:4-9; Dt 30:14; Ro 10:8; Dt 32:46; Ps 37:31; Ps 40:8; Pr 6:21; Pr 7:2-3; Jer 31:33
The practice of wearing phylacteries
Mt 23:5 Jesus Christ condemns the Pharisees for wearing phylacteries for outward show.