The fifth aliyah establishes the idea of the prophet of Israel. Because at Mt. Sinai the Jewish people claimed they couldn't hear G-d's voice directly, G-d here says that He will raise up prophets and that G-d will put words into their mouth. We are commanded to listen to the prophets.
Also in this aliyah is a reiteration of the command to establish cities of refuge for the inadvertent killer and some laws of murder.
