The Punishment of Double, Triple and Quadruple for Theft (Mitzvah 54)
The penalty for stealing is that the thief has to pay back double. Buying stolen goods is listed by the Rambam Hilchot Teshuva as an unrepentable sin (because you won't be able to pay back the original owner).
The Rambam in the Moreh Nevuchim discusses the reason for penalties - deterrence (e.g. double for theft, death penalty for a murderer). Other explanations, from the Ibn Ezra (hindering the means of production), Chizkuni, Torah Temimah, and the Akeidat Yitzchak.
Why robbery (חמס) is so heinous that it warranted destruction of the world.
Delivered at the OU Israel Center, Wednesday, November 21st, 2018/13 Kislev 5779