God sees the wound in the family of Adam and Eve. Seth takes Abel’s place. Even more clearly than at the birth of Cain, Eve recognizes God’s work in this birth. Adam and Eve had more children (remember Cain’s fear of everyone,
Genesis 4:14). Seth is mentioned here because he takes Abel’s place and thus is God’s comfort after the terrible fatal quarrel between the brothers. The Cains
of this world can win it over and wipe out the Abels
of the faith. But God continues their line for all eternity. They are ultimately (more than) conquerors (Romans 8:37). Seth also becomes the person in which God continues the line of the patriarch of mankind. He gets the birthright, so to speak. That does not always automatically go to the eldest, think of Jacob (Genesis 27:1–46), Ephraim (Genesis 48:13–14), and Joseph (Genesis 49:26).
25 And Adam knew his wife again, and she bore a son and called his name Seth, for she said, “God has appointed for me another offspring instead of Abel, for Cain killed him.”