Genesis 3 :
14. So the Lord God said to the serpent:
"Because you have done this,...
15. ... I will put enmity between you and the woman,
and between your seed and her Seed;
He shall bruise your head,
and you shall bruise His heel."
New King James Bible
The setting here was the Garden of Eden. God was dealing with the situation created when Adam and Eve obeyed Satan instead of God.
This is the first time God states very clearly that He will send the Messiah, the Saviour, into the world. This is the first time we hear about Christmas.
God tells Satan that He will send Someone who will be the seed of the woman.
This Someone will bruise the head of Satan. That means He will deal a death-blow to Satan in his head.
On the other hand, Satan will be able only to bruise His heel. The heel represents a vulnerable place in the human body, which can bring a person down, but not deal them a death-blow.
God was showing that Satan would bring Jesus down - through death - but death would not be able to hold Him as it does other human beings.
On the other hand, the death of Jesus would strike Satan and his kingdom in the head, giving him the death blow.
Because Jesus rose from the dead, death was just a bruise on His heel. Praise God!
Now Jesus is in the place of power in heaven with our Father, gathering us into His kingdom and purpose, and taking us out of the hand of Satan, whom Jesus has already crushed.
Father, thank You that from the beginning of human history You had a plan to deal with Satan's meddling in the human race.
Your solution began when You sent that special Someone at Christmas: the Lord Jesus Christ.
Lord Jesus, I thank You that You faced death for me, and for You it was only a bruise on Your heel, because You came right back from it.
Thank You that because You did this, I do not have to fear death today, since I put my trust in You.
In Your name I pray, Amen.