Genesis 4:2

And she again bare his brother Abel
Or "added to bare" ^F25, not directly or immediately, but perhaps the following year; though some have thought, because no mention is made of her conceiving again, that she brought forth Abel at the same time she did Cain, or that the birth of the one immediately followed upon that of the other: and it is the common opinion of the Jews ^F26 that with Abel, as with Cain, was born a twin sister, whom the Arabic writers ^F1 call Lebuda: the name of Abel, or rather Hebel, signifies not "mourning", as Josephus ^F2 observes, but "vanity", Eve not making that account of him as she did of Cain; or perhaps because by this time she became sensible of her mistake in him, or had met with something which convinced her that all earthly enjoyments were vanity; or by a spirit of prophecy foresaw what would befall this her second son, that he should be very early deprived of his life in a violent manner:

and Abel was a keeper of sheep:
a calling which he either chose himself, or his father put him to, and gave him; for though he and his brother were born to a large estate, being the heirs of Adam, the lord of the whole earth, yet they were not brought up in idleness, but in useful and laborious employments:

but Cain was a tiller of the ground:
of the same occupation his father was, and he being the first born, was brought up in the same business, and might be a reason why he was put into it.