For the rest of the world, these laws are based on civility and pragmatism. In truth, no society can exist without some code of accepted behavior, but the difference in the origin of such law between the Torah and every other society is an enormous and fundamental one. No man-made system of laws can withstand the onslaught of a person's baser instincts. Rivers of innocent blood have flowed in wars in every era, including our own, in spite of the fact that a prohibition against murder is a universally accepted tenet. That one letter, the vav that connects this week's Parsha and last week's, defines what gives the Torah's code of social justice its strength and durability over three thousand years after its institution - divine origin.
All bullies are cowards.
When someone feels there's nobody to stop him from doing what he wants, he can become a tyrant. If there's someone standing over him waving a big stick, even a tyrant will think twice. That's the connection between this command not to oppress a stranger and the Jewish People being strangers in the land of Egypt. Pharaoh felt free to oppress the Jewish People because he thought there was no one to stand up for them. No Big Stick.