"And you shall bind them [the words which declare our love for God] for a sign upon your hand and they shall be as frontlets between your eyes".
We are commanded to bind the words "And you shall love HaShem your God with all your heart and with all your soul and with all your might" upon our hands and between our eyes. This means that love for God must influence what we do with our hands--our actions--and what we think with our brains--our thoughts.
This and the previous verse together (see here) teach us that our love for God must make us speak, do, and think what is right.
This verse is the origin of the use of the Tefilin or phylacteries, which contain four sections of the Tora, which set forth all that is dear and holy for the Jewish people. They are worn, therefore, because of what they teach and because of their influence, when rightly understood, upon our conduct. Similarly the High Priest wore on his forehead the inscription "Holy to HaShem," to teach holiness as the ideal of human conduct.
"Wearing" the Shema Israel as a frontlet thus becomes a reminder of right conduct through love of God.
These ideas are conveyed in the words of the meditation which many Jews recite when about to wear Tefilin: "Through the influence of this command, the Tefilin, may we be blessed with sacred impulses and pure thoughts, with no desire for sin or iniquity. May evil imagination have no power to allure us and lead us astray, but may we be led to worship HaShem as it is in our hearts to do."
Adapted from the book "Jewish religion ethically presented" by rabbi Hayim Pereira- Mendes (1905)
Click here to read: "TEFILLIN: Everything you need to know about those powerful black boxes, placed on the head and arm" by Rabbi Shraga Simmons, from Aish.