Here's the story:
Asa became King of Judah and had a rocking relationship with God. He was very effective and changed Judah for the better, turning the country back towards the Lord and away from idols. At one point, ten years into his reign, King Asa and his army are up against one million soldiers. He prays to the Lord, acknowledging that without God, he has no chance of winning the battle. God comes through, and Judah wins the battle.
Twenty-six years later, King Asa is faced with a similar situation. It's not one million soldiers, but a foreign king is threatening the kingdom. Instead of praying to God, he takes treasures (some of them from the temple) and buys his way out of his tough position. While his buy-out is successful, God sends a prophet and clearly tells King Asa that he was in the wrong, since he didn't rely on God as he once did.
(Full version of the story here)
I'm sure there is more than one take-away for this story, but here's mine and it comes in the form of a warning:
The longer you are doing something, the harder it is to continue relying on God while you do it.