The thread running through Genesis of a coming offspring (zera', "seed") who will crush the serpent's head (Genesis 3:15), through whom all nations will be blessed (Gen 12:3, 22:18), and to whom the throne is ultimately given (2 Samuel 7:12-14, Psalm 72, Isaiah 11). The seed is a corporate and ultimately singular figure — Paul makes this explicit in Galatians 3:16: "Now the promises were made to Abraham and to his offspring. It does not say, 'And to offsprings,' referring to many, but referring to one, 'And to your offspring,' who is Christ."
The seed promise is the Bible's single unifying thread. Every major narrative turn in Genesis is a threat to the seed line: Abel is killed, Sarah is barren, Rebekah is barren, Rachel is barren, the seed enters Egypt under threat of famine, Pharaoh orders the Hebrew boys drowned. God protects the line against every assault — because the serpent knows that when the right Seed comes, its head gets crushed. Matthew opens his Gospel by tracing the seed line from Abraham to David to the exile to Christ (Matthew 1) — saying, in effect, "the Seed has arrived." Galatians 3:29 closes the loop for the Church: "If you are Christ's, then you are Abraham's offspring, heirs according to promise." The blessing of the nations has come true in the Messiah, and by union with Him we are incorporated into the seed. Eschatologically, the final crushing of the serpent is still pending: "The God of peace will soon crush Satan under your feet" (Romans 16:20).