One of the key moments in the entire biblical story appears in this week's reading, with what is known as the Sin of the Spies. After taking the Israelites out of Egypt and giving them the Ten Commandments, God now tells Moses to send twelve men, representing each tribe, to reconnoiter the Promised Land in advance of the invasion that is meant to complete the exodus.

But something goes wrong. They come back not with battle plans but with a plea to call the whole thing off. "The people are strong who dwell in the land, and the cities are fortified, and very great. . . . We were in our own sight as grasshoppers, and so we were in their sight" (Numbers 13:28-33).  Panic spreads, and soon the whole nation is beset with terror.

On the face of it, their worries are absurd. The Israelites' hundreds of thousands of fighting men would have overwhelmed the puny indigenous towns, no matter how high their walls. Yet for a slave nation that has never really had to defend itself militarily, much less launch an invasion, the prospect of fighting is too much to bear. "And all the congregation lifted up their voice and cried. . . . ‘Would that we had died in the land of Egypt! . . . Why has the Lord brought us to this land, to fall by the sword, that our wives and our children should be a prey?'" (14:2-3)

Of all the Israelites' backslidings in the desert journey, none—not even the Golden Calf—exacts so dire a punishment as the sin of the spies. Livid, God tells the entire adult population that "Your carcasses shall fall in this wilderness, and all that were numbered of you . . . shall by no means come into the land." The Israelites are destined to wander the desert until the generation wholly passes away. A trip that was meant to last just a few weeks will now take four decades.

What is it that makes the Israelites not only unworthy of the much-promised Promised Land but destined to wander the desert like ghouls awaiting their final rest?

To answer, we need to look at the only other place in the Torah where such a punishment is meted out: in the sin of Cain. Just like the Israelites this week, Cain, who murders his own brother Abel in a fit of jealous spite when God prefers the latter's offering, is sentenced to a life of indigent wandering. In response to the slaying, God announces that from now on, the fields will no longer produce food for Cain. "A fugitive and a vagabond shall you be on the earth" (Genesis 4:12).

The sins of Cain and of the spies may strike us as utterly different—murder in the one case, disobedience in the other. Yet something ties them together. In both cases, the sinner has allowed his spirit to collapse utterly, losing his bearings and falling out of touch with the bold, creative, self-affirming spirit that is the touchstone, we understand, of our humanity.

In some sense, their wandering is as much a natural consequence of their deeds as it is a punishment for them. What are we worth if we let self-loathing commandeer our actions or dictate our most fateful decisions? At the end of the day, our lives may become a series of soulless wanderings. Like Cain and the Israelites, we forget that goodness requires not only refraining from sin but resolute action—and resolute action, in turn, requires an inner fire, a quality of self-love, that, by themselves, discipline and self-control cannot supply.

David Hazony's first book, The Ten Commandments: How Our Most Ancient Moral Text Can Renew Modern Life, will be published by Scribner this coming September.