The Shema paragraph (Devarim 6:4-9) consists of three sections: 1) the principle of faith; 2) the meaning of this principle in our lives; 3) guidance on imbuing our lives with faith.
1) The first verse, “Hear O Israel, the Lord our God, the Lord is One,” teaches the core principle of Jewish monotheistic faith: that God is Master of all and there is no power in the world other than Him. Even though it may seem to us that there are other distinct powers, in truth God is the One and Only, Who sustains all. There is none but Him.
2) This belief bears great significance on our lives. It implies that there is no value in this world outside adherence to God, and we are thus enjoined to love Him “with all your heart, with all your soul, and with all your might.” The Sages (Berakhot 54a) interpret these words: “‘With all your heart’ – with both of your inclinations: your good inclination and your evil inclination,” because one’s evil inclination must be controlled to serve God, whether by force or by transforming it into good; “‘And with all your soul’ – even if it takes your life,” for one must be ready to give his life for his belief in God; “‘And with all your might’ (‘me’odekha’) – with all your money (‘mamonekha’)” – even one’s money should serve as a basis and a means to serve God, 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. Alternatively, they interpret, “‘With all your might’ – no matter what He metes out to you (‘be-khol mida u-mida she-Hu moded lekha’), be very grateful to him.”
3) In the third part of this paragraph, the Torah offers guidance for incorporating these principles of faith. First, “These words that I command you today shall be upon your heart,” and then, “teach them to your children.” Even after one learns the basics of faith very well, if he does not repeat them to himself every day, the worries of his life and his dealings can cause him to forget them. Therefore we are commanded, “And you shall speak them when you sit at home, when you walk on your way, when you lie down, and when you rise.” From here we derive the obligation to recite Shema both in the morning and at night. Nevertheless, the Torah is not content with recitation alone; it adds the mitzva to place these paragraphs on faith into our tefillin and to bind them to our arms and heads: “You shall bind them as a sign on your arm and they should be a symbol between your eyes.” We are moreover commanded to fix them firmly in the mezuzot on our doorposts, as it is written, “write them on the doorposts (mezuzot) of your homes and your gates.” This is so that every time we enter and exit our homes, we notice the mezuza and recall the fundamentals of Jewish faith.