It is my policy not to answer a "why" question regarding the motive of others unless their intentions have been provided, except in a most tentative manner. In other words, since we do not seem to be provided with the "why" of Abel's actions, any answer will at best be speculative. To presume why people do the things they do without them saying why is an example of the "unrighteous judgment" that Jesus warned against:
NASB John 7:24 "Do not judge according to appearance, but judge with
Righteous judgment requires abilities that most of us lack:
NASB 1 Samuel 16:7 But the LORD said to Samuel, "Do not look at his
appearance or at the height of his stature, because I have rejected
him; for God sees not as man sees, for man looks at the outward
appearance, but the LORD looks at the heart."
NASB 1 Kings 8:39 then hear in heaven Your dwelling place, and
forgive and act and render to each according to all his ways, whose
heart You know, for You alone know the hearts of all the sons of men,
So to answer the question I would say that I don't know nor does anyone else. However, we can ruminate and speculate.
Also, the Hebrew does not indicate that the animal(s) he tended were sheep. The word used merely indicates that they were small flock animals which in Moses' time would suggest sheep and/or goats together in one flock. Christians tend to assume that they were sheep because of some mistaken belief that sheep were God's preferred sacrifice. However, I don't believe that sheep were a special animal in that regard in the Torah.
However, while both goats and sheep provide milk (and therefore cheese) only sheep provide wool. It appears that sheep wool has been used in the making of clothing from time immemorial:
So why might he have tended a flock?
First I would mention why some of the other suggestions made here might not be on point:
it is unlikely that any animals in the domain were naturally dependent on care from humans, as was suggested. Wild sheep and goats do not need to be sheared or have their hooves trimmed. Hooves wear down from use in the wild. The uncontrolled growth of domesticated sheep is a product of selective breeding.
YHVH did not provide an example of shearing sheep to make clothing. Either, as I am inclined to believe, the covering that YHVH provided to Adam and Eve was for the covering of their skin in the form of pubic hair... This would be similar to the provision of hair as a natural covering to woman's head:
NASB 1 Cor 11:15 but if a woman has long hair, it is a glory to her?
For her hair is given to her for a covering.
Or, the animal's skin was given as the covering, not the wool. Either way, Abel was not imitating YHVH directly. They would be imitating in making clothing but from wool not from skin unless they skinned the animal, in which case the animal was raised for its hide, not its wool. In that case sheep or goat would not matter.
RevelationLad's musings that the gift of the animal to YHVH may have been offered as a living sacrifice makes a lot of sense in the context of Genesis. However, if we consider Hebrews 11:4 the word θυσίαν (sacrifice) is used which from an "NT colored perspective" suggests that the animal was killed. Regardless it is an excellent and well reasoned suggestion and we do have Paul suggesting that a living sacrifice (θυσίαν ζῶσαν) which, unlike Cain's offering (and like Abel's offering) was acceptable to God, suggesting an allusion. So ultimately right or wrong, his answer gets a +1 from me.
the idea that he kept animals specifically for sacrifices and not as a livelihood is, I think, not in keeping with the juxtaposition with Cain's livelihood:
NASB Genesis 4:2 Again, she gave birth to his brother Abel. And Abel
was a keeper of flocks, but Cain was a tiller of the ground.
The objection that YHVH forbade drinking animal products assumes that:
- the announcement that they were given plants for food was tantamount to a prohibition of consuming animal products was not a given (https://youtu.be/ZGZLM0FrcwE?t=50s)
- the Adam family, strapped by a cursed land, didn't seek out other sources of nourishment than that provided might again not be a given
So if pressed to speculate I would speculate that either:
- this is an accidental anachronism by the author
- Abel kept flock animals as his livelihood by exploiting their wool for clothing and possibly also their milk for drinking
- cheese making seems anachronistic
- trade other than division of labor within the family seems anachronistic
- sacrificing wool and milk are probably not sufficiently better than offering grains to make his sacrifice more dear than Cain's given that food was grown with difficulty under the curse
- offering an animal that he had raised from birth would be a somber and heart wrenching sacrifice and is likely but is not likely why that was his livelihood. However, releasing the animal into the wild, as on Yom Kippur might have likewise been very difficult with an animal. I have heard that the attachment of shepherds with their animals is very much that of beloved pets.
Again, I don't think we are told so the above are just my ruminations and speculations.