Its main content is loving the one God with all one's heart, soul and might, and the rewards that come with this.
The term "Shema" is used by extension to the whole part of the daily prayers that commences with Shema Yisrael and comprises Deuteronomy 6:4–9, 11:13–21, and Numbers 15:37–41.
And these words, which I command thee this day,
And thou shalt teach them diligently unto thy children,
And thou shalt write them