The Shema paragraph (Deuteronomy 6:4-9) consists of three sections: 1) the foundation of faith, 2) the meaning of this foundation in our lives, and 3) instructions on how to instill faith into our lives.
1) From the first verse, “Hear O Israel, Hashem is our God, Hashem is One,” we learn the foundation of the unifying belief of Israel, that Hashem Blessed Be He is the Master of everything, and there is no force in this world other than He. Even though it may seem to us that there are other distinct powers, separate from one another, Hashem, Who is One, sustains all life, and there is no one else.
2) The significance of this belief in our lives is that there is no other value in this world aside from the devotion to Hashem Blessed Be He. Hence, “Love Hashem your God with all your heart, with all your soul, and with all your might.” The Chachamim (Berachot 54a) interpret these words: “With all your heart” – with both your inclinations: your good inclination (yetzer hatov) and your evil inclination (yetzer hara), – because one’s evil inclination must also be controlled to serve Hashem, whether by force or by transforming it into good. “And with all your soul” – even if it takes your life, for a person must be ready to give his life for his belief in Hashem. “And with all your might” – with all your resources; even a person’s money should serve as a basis and a means to serve Hashem, so that if it were demanded of a Jew to violate his religion or lose all his wealth, he would forfeit his money rather than defy his belief. Additionally, they interpret, “With all your might” – for each and every measure that Hashem bestows upon you, be grateful to Him very very much.”
3) In the third section, the Torah instructs us regarding how to instill these foundations of belief in ourselves. First, “Put these words that I am commanding you today into your heart” and additionally, “Teach them to your sons.” Even after a person learns the basic tenets of faith very well, if he does not repeat them to himself every day, life’s dealings and worries can cause him to forget them. Therefore we are commanded, “And say them when you sit in your house, when you walk on your way, when you lie down and when you rise up.” From this we learn the obligation to recite Shema both in the morning and at night. Nevertheless, the Torah does not suffice with its recital alone, but rather adds the commandment to place these paragraphs of belief into our tefillin and to bind them on our arms and heads, as it is written, “And you shall bind them as a sign on your arm and they should be as frontlets between your eyes.” We are also commanded to fix them firmly in the mezuzot on our doorposts, as it is written, “And write them on your doorposts of your houses and your gates.” This is so that every time we enter and exit our houses, we look at the mezuzah and are reminded again of the foundations of Israel’s faith. Thus, the paragraph that discusses belief and the oneness of the Creator constantly guides us, in our hearts with Keriat Shema, on our bodies through tefillin, and on our property, meaning our houses, via the mezuzah.