2 Chronicles 32-33: With Him is Only the Arm of Flesh

After all that Hezekiah had so faithfully done, Sennacherib king of Assyria came and invaded Judah. He laid siege to the fortified cities, thinking to conquer them for himself. - 2 Chron 32:1 NIV  Sennacherib thought he was invincible. 

Hezekiah did not.  With him is only the arm of flesh, but with us is the LORD our God to help us and to fight our battles." 2 Chron 32:8

This battle, the battle between God's chosen people and his enemies, the battle for power, the battle between good and evil has been going on since the beginning of time.  Even before the beginning of time as we know it, there was one who thought he was invincible

How you have fallen from heaven,
O morning star, son of the dawn!
You have been cast down to the earth,
you who once laid low the nations!
You said in your heart,
"I will ascend to heaven;
I will raise my throne
above the stars of God;
I will sit enthroned on the mount of assembly,
on the utmost heights of the sacred mountain.
I will ascend above the tops of the clouds;
I will make myself like the Most High." - Isaiah 14:12-15 NIV

The same end that came to Lucifer, the prince of heaven, came to Sennacherib and all who oppose God.

But you are brought down to the grave,
to the depths of the pit.  - Isaiah 14:16 NIV

Hezekiah knew it, any Old Testament king that was invincible knew it, only God has the power to have the final say.