I disagree with most of what Sarna is saying here:
Nahum M. Sarna in the The JPS Torah Commentary: Genesis said:
This narrative has often been interpreted as a reflection of the traditional conflict between the farmer and the nomad, and its supposed bias in favor of the latter is seen as representing a nomadic ideal in Israel. This is unlikely. The evidence for such an ideal in the biblical literature is extremely flimsy.
I think there's a strong pro-nomadic sub-text throughout the entire Tanakh/Old Testament:
http://www.religiousforums.com/forum/2989260-post6.html
Further, there is not the slightest suggestion in the text of any comparative evaluation of the vocations of Cain and Abel, nor is there the slightest disparagement of the tiller of the soil.
I think the idea that God honors Abel's sacrifice but rejects Cain's could be interpreted as His preference for one mode of life over another.
On the contrary, agriculture is regarded as the original occupation of man in the Garden of Eden as well as outside it.
Disagree with this too. Genesis does say in several places that Man is to eat herbs, fruit, plants in general, but there's nothing to indicate that Man has any role in the production of any of it (except for one brief passage in Gen.1). It could just as easily be interpreted as another endorsement of the Hunter/Gatherer existence as it could be an agrarian one.
On the other hand, the curse that God lays on Adam sounds (to me) like a pretty good description of the agrarian lifestyle:
Gen: 17 Then to Adam He said, “Because you have heeded the voice of your wife, and have eaten from the tree of which I commanded you, saying, ‘You shall not eat of it’:
“Cursed is the ground for your sake;
In toil you shall eat of it
All the days of your life.
Which seems to suggest that there was no work involved in the consumption of plant foods prior to the curse.
Same here:
Gen:18 Both thorns and thistles it shall bring forth for you,
And you shall eat the herb of the field.
19 In the sweat of your face you shall eat bread
The sentence upon Cain is restricted to him alone;
The text has God condemning Cain to a life as "A fugitive and a vagabond", an outcast, not a nomadic herdsman.
his sons are not made into vagrants or stigmatized in any way. Finally, the three pillars of semi nomadic culture, as set forth in verses 20-22, are actually said to have originated with the descendants of Cain.
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He's talking about this:
Genesis 4:20 And Adah bore Jabal. He was the father of those who dwell in tents and have livestock.
I don't think the fact the fact that one of Cain's (fairly distant) descendants became a nomadic herdsman contradicts the theme. The same verse goes on to identify two brothers of Jabal as the "fathers" of music and metallurgy, two by-products of civilzation.
Gen:21 His brother’s name was Jubal. He was the father of all those who play the harp and flute. 22 And as for Zillah, she also bore Tubal-Cain, an instructor of every craftsman in bronze and iron.