What is known as the protoevangelium or the first gospel is found in Genesis 3:15. This is the first promise of salvation.
(Genesis 3:15)"I will put enmity between you and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel." (ESV)
This verse in found in the context of God pronouncing the curse on the serpent. The serpent is of course the devil or Satan (See Revelation 20:2). The serpent received this curse because he deceived Eve and led Adam and Eve to sin against God, bringing all humanity and creation under the sin curse. This is known as the Fall.
The offspring of Satan includes all unbelievers while the offspring of the woman (Eve) includes Christ and all believers. He in the last part of the verse refers to Christ. Jesus will bruise the devil's head, that is crush or destroy him. Satan will only bruise the heel of Christ, that is cause suffering.
Jesus through his life, death, and resurrection has defeated the devil, sin, and death. The victory will be consummated at the Second Coming of Christ.
