Genesis 4:25

“Adam made love to his wife again, and she gave birth to a son and named him Seth, saying, ‘God has granted me another child in place of Abel, since Cain killed him.’”  Genesis 4:25

While Cain is going off and building cities and growing his line, Adam and Eve have a third son.  Did they have no other children between Abel and Seth?  From the sound of the story it looks like Cain and Abel were at least teenagers when Cain killed his younger brother and we don’t know how long after the murder that Seth was born, but that’s a pretty big gap between kids.

Did Cain go meet his wife before Seth was born?  If she was also a daughter of Adam and Eve when was she born?  How many years was Cain alone, before his sisters were born and old enough to marry?

Whatever the case, God gave Adam and Eve comfort from losing one child by giving them another.  Anyone that has ever lost a child knows that nothing can ever take the place of the dead child, but for Eve, anyway, the pain was eased and comfort found with a new baby.

The death of their son must have really drove home God’s original command to not eat from the tree of the knowledge of good and evil that death would follow.  Even if they intellectually understood at this point what death is, often you can never really understand until you experience it.  And now they were seeing the consequences of their disobedience affecting, not just them, but their sons also.

Seth was a new chance from God to raise this son right.  Even if Cain repented and lived the rest of his life as a saint, he was no longer with his parents and they would have little more influence on him.  Besides he was the one that took Abel from them in the first place.  I imagine it would be difficult for them to want him around after that even if they did forgive him.