Why is Cain “cursed from the earth” (Gen 4:11) by God?

In short, and in terms of the figure, it is because he shed blood on the ground: life is sacred, so the blood of life is sacred, and so the shedding of life blood is absolutely forbidden and brings a curse. Since Abel’s blood was spilled on the same ground from which Cain earns his living, the blood is cursed from that ground. Moreover, Cain’s offering was the first fruits of the ground, and so he was punished in respect of his work—that is, from the ground out of which his offering came. No future offering from that source would be acceptable, which is why the ground would no longer produce crops for Cain.