The Three Paragraphs of Shema

The three paragraphs of the Shema prayer, each have their own message. Collectively, they make up one of the most important prayers of the Siddur.
The first paragraph speaks primarily about the Oneness and uniqueness of Hashem. We accept that there is none like Him, and his holiness is not like any other being in the universe.
The second paragraph, והיה אם שמוע, emphasizes the acceptance of עול מלכות שמים, the yoke of the kingdom of Heaven. After acknowledging the awesomeness of our Creator, we accept the obligation placed upon us, to fulfill all that is demanded of us.
This includes the necessity to observe both the Written and Oral Law, and it means that we will similarly observe the commandments that we don’t understand and do not seem logical to us.
It is for the latter type of Mitzvot that we receive the greatest reward. The only reason why we choose to observe these commandments, is because we accept upon us, the yoke of Heaven.
The third paragraph speaks of the Mitzva of Tzitzit. Wearing a four cornered garment with fringes, serves as a constant reminder of our obligation as Jews. It also reminds us to remember that G-d took us out of Egypt. When we began as a nation, Hashem showed that He existed, and revealed Himself in an outward fashion.
We can see why the messages of each paragraph of Shema, make it such an important and special prayer.