Va'etchanan - Shishi
This aliyah starts with the Shema, perhaps the most recognized phrase in Judaism: "Listen, Israel - God is our Lord; God is One."
Israel was then told to love God whole-heartedly, with every aspect of their existence. They were to speak words of Torah constantly, repeating the Shema and internalizing its message every morning and every night. It would also be written in the tefillin that a Jewish man wears on his head and arm, as well as in the mezuzah on every Jew's doorpost.
The nation was warned about the dangers of complacency. When everything is going well, there's a tendency to forget about God. They must be careful not to do this. If they leave Him and stray after idols... well, let's just say it won't be good.
The Jews were also warned not to provoke God. If they follow His mitzvos, they will enjoy a good life, secure in their land. In the future, the Jews' descendants will ask why they do all these things; they are to answer that it is because God rescued the nation of Israel from Egyptian slavery and brought them to their own land. It is a privilege to be able to fulfill His will. (Verse 20 is the question of the wise son in the Passover Haggadah; verse 21 is the start of the leader’s response to the Four Questions asked by the youngest.)