The Protoevangelium — Genesis 3:15

Gen 3:15, the protoevangelium, promises enmity between the serpent and the woman's offspring: "he shall bruise your head, and you shall bruise his heel." In the midst of the curse, the first gospel is spoken.

Irenaeus — Against Heresies, and John Calvin — Institutes of the Christian Religion. The bruised heel anticipates the cross; the crushed head, the resurrection.

The promised seed is traced through the Abrahamic covenant of Gen 15:5 and fulfilled in the woman's son of Gal 4:4. The serpent's final defeat is sealed in Rev 12:9.