Halakhah zu Dewarim 6:4

The foundation of Torah and the pillar of the divine service is to know that there is one God. who is singular and unique, and that He created the Worlds(i.e this world and the next world), and that he is constantly watching us. If, God forbid, he suddenly stopped watching and guiding the world even for a moment, it would revert to chaos and disorder. This is the essence of what is stated: (Deuteronomy 6:4) 'Listen, oh Israel, Hashem, your God, is One'.

The recitation of Shema includes three paragraphs. The first is “Shema” (“Listen”; Devarim 6:4-9), in which we accept the yoke of heaven and which discusses God’s unity and our love for Him. The second is “Ve-haya im Shamo’a” (“And if you follow”; Devarim 11:13-21), which contains the acceptance of the yoke of the mitzvot. The third is “Va-yomer” (“And He said”; Bamidbar 15:37-41), within which there is a command to remember the mitzvot via the mitzva of tzitzit, and at the end of which the Exodus from Egypt is mentioned.