Charles Ellicott Commentary Genesis 4:25

"And Adam knew his wife again; and she bare a son, and called his name Seth. For, [said she], God hath appointed me another seed instead of Abel; for Cain slew him." — Genesis 4:25 (ASV)

SUBSTITUTION OF SETH FOR ABEL.

Another seed instead of Abel, whom Cain slew. —Cain, the firstborn, and Abel, who had outstripped him in prosperity, were both lost to Adam. But instead of the third son succeeding to the place of the firstborn, it is given to one specially marked out, probably by prophecy, just as Solomon took the rights of primogeniture over the head of Adonijah.

Seth. —Hebrew, Sheth, that is, appointed, substituted; he was thus specially designated as the son who was to be the chief over Adam's family.