Symbolism, Imagery, Allegory
A book full of laws being packed full of judicial imagery? Gasp! It can't be!
Okay, we know, it's not that surprising. But we're not just talking about Moses appointing judges or talking about how many witnesses are necessary for conviction. In Deuteronomy, there are some fancy symbolic witnesses, too. Twice Moses calls heaven and earth to witness against the Israelites (4:26 and 31:28).
The prosecution would like to call heaven and earth to the witness stand!
Sounds weird, right? But who else is left? Moses is representing God, the other party in the covenant with Israel. Israel can't be a witness because they're involved in the trial, and the other nations are too wicked. Heaven and earth are the only ones available. It's kind of like Jack McCoy pulling a surprise witness out of his hat forty-nine minutes into an episode of Law & Order—just enough time to snag a conviction from the jaws of defeat.
Notice how Moses makes a clever use of symbolic language here. Basically, he creates a courtroom out of thin air. If the Israelites fail to keep up their end of the contract with God, rain won't fall from the heavens. If they are loyal, they can break out their umbrellas (11:11-14). In a society so reliant on crops, rain was life.
One last note: Moses is firmly on God's side throughout all of this. Why? Seriously, we're asking: why would he take God's side after the guy just forbade him from going into the Promised Land?