After the Fall of Adam in the Garden, God pronounced judgment on the devil    and was seen symbolically in the animal that he had embodied the serpent.  The serpent would illustrate the devil being dishonored as the serpent would be loathed and crawl on it's belly in the dirt.  We see the First Gospel through the great promise of a coming Redeemer, the Lord Jesus Christ who 's heel would be bruised by Satan, but the Lord would crush his head in victory over him.  This is the victorious work of Christ on the cross as He died for sinners and rose again, so was victorious over sin thus crushing the head of the devil.

Primary Scripture: Genesis 3:14-15