“five oxen for an ox, and four sheep for a sheep.” Here in Exodus 22:1, the Torah teaches us that not all property has the same value. We know this, of course. There are things that do not mean much to us, and other things that mean a lot and/or are more inherently valuable. A thief who steals a more valuable thing is required to pay more.
In this example, an ox is more valuable than a sheep both inherently, and also because it is likely that the owner of the ox would have spent considerable time training it to pull carts and such, and to plow. Stealing is very harmful to a society, and God takes it very seriously. If a thief cannot repay the debt he owes from his theft, then he is sold into slavery for six years and goes free in the seventh (Exod. 22:3; 21:2). Modern society also makes people a kind of slave: we put them in prison where their life is not their own. They do, wear, eat, and sleep, what they are told to, and when their sentence is up they go free. Sadly, modern society often does not take stealing seriously, and thieves get little or no meaningful punishment, which only encourages more stealing.
If the thief still has the thing that he stole when he is caught, he still has to compensate for the anxiety and effort of the person he stole from and the society he damaged. He must give back what he stole and add one to it, thus paying “double” (Exod. 22:4). For example, if the person stole a sheep, then he would give back the sheep and add one more sheep as well.
To understand some of the anxiety and effort caused by stealing it helps us to remember that in ancient times there was no police force. If something was stolen from a person, that person had to track down the thief himself, which usually meant taking considerable time, and also enlisting the help of friends and neighbors. The thief then had to be forcibly brought—often no easy task since the thief knew what was coming—before the local judges who would make a decision about the matter and determine if there was really a theft and if so what was stolen. We can imagine that that decision was often not easy, and enforcing the penalty was also not easy. The best course people had then, and now as well, was to be diligent to protect their things in the first place.