Peter Laarman makes the theological case:
We are all compounded of bits of good and bits of evil in a complicated admixture. And so trickster Jacob is not ultimately damned on account of his trickery in displacing his older brother’s inheritance, nor is King David ultimately damned for arranging to murder the warrior husband of his desired inamorata. The great European-American epic poets and novelists who inherit both the Hellenic and Hebraic traditions tend to favor the Hebraic mode of shadow and inference. They are not especially interested in presenting us with any “pure” types: in giving us unalterably evil or incorruptibly good characters who never vary, never change it up.