John Calvin 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)

Adam knew his wife again. Some from this infer that our first parents were entirely deprived of their offspring when one of their sons had been killed, and the other was banished far away. But it is utterly incredible that, when the blessing of God in the procreation of humankind was in its full strength, Adam and Eve should have been unfruitful for so many years.

But rather, before Abel was killed, the continuous succession of offspring had already made Adam's household populous; for in him and his wife especially, the effect of that declaration should have been evident: Increase and multiply, and replenish the earth. What, therefore, does Moses mean? Indeed, that our first parents, horrified at the wicked killing, abstained for a time from marital relations.

Indeed, it could hardly have been otherwise; in reaping this extremely sad and bitter fruit of their apostasy from God, they must have sunk down almost lifeless. The reason he now omits others is that he intended to trace the generation of pious descendants through the line of Seth.

In the following chapter, however, where he will say that Adam begat sons and daughters, he undoubtedly includes a great number who had been born before Seth. Little regard is given to them, however, since they were separated from that family which worshipped God in purity, and which might truly be considered the Church of God.

God, she says, has appointed me another seed instead of Abel. Eve means a special seed; for, as we have said, others had been born who had also grown up before Abel's death. But since the human race is inclined to evil, nearly her whole family had, in various ways, become corrupt. Therefore, she had little hope for the remaining multitude, until God would raise up for her a new seed, from whom she might expect better things. Therefore, she regarded herself as deprived not of one son only, but, in the person of Abel, of her whole offspring.