The earliest reference to Christ in the flesh is found in Genesis 3:15, that's right, Genesis!  That verse reads "And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel."
    This verse follows the sin of Adam and Eve, and is spoken by God to Satan.  This is clearly a reference to Christ and His death upon the cross.  Notice that the verse speaks of "her seed."  The seed is in the man, but since the birth of Christ by Mary would be a virgin birth it is appropriately stated "her seed" in this verse.
    As for the death of Christ and how it relates to this verse, it can be said that Satan's greatest victory occurred when Christ was hanging upon the cross, lifeless.  God makes the point though that Christ's death would not be the end.  The death on the cross would merely bruise His heel, for He would arise from the dead on the third day.  That event would signal the defeat of Satan, it would bruise Satan's head, or more accurately crush his head.
    This verse then is more than an idle statement from God to Satan, it is a prophecy of Christ' birth (Matthew 1:18-25; Luke 1:26-35; John 3:16-18), of His death (Matthew 27:50; Luke 23:33; I Peter 2:22-24), of His power over the grave (Matthew 28:5,6; Acts 2:32; 5:30; 10:40; 13:29,30; II Corinthians 5:14,15), and ultimately of the redemption of men since we are saved by His death on the cross (Romans 6:4; Hebrews 9:22; John 1:29; Revelation 1:5; Hebrews 9:15-17).