2 Samuel 24 - David's biggest mistake

This was probably David's greatest mistake. The Lord was angry with Israel. Now it is very interesting that here it implies God incited David to take the census, whereas in 1 Chronicles 21:1 it says Satan incited David. This gives us insight into interpreting the Bible. God is Lord of all and is ultimately in control of everything, nothing happens that is beyond His control. This is the aspect represented here. At the same time men (and devils) are responsible for their own actions, and that is the aspect represented in Chronicles.

We now read how the incident unfolded. David told Joab to count all the fighting men. Joab advised against doing this, given his previous behaviour, this is one of the few times when David would have done well to follow Joab's leanings.
However, the process went ahead and it took just under ten months to complete. Only after he had completed the exercise did David realise how foolish and wrong he had been. God spoke to the prophet Gad, and Gad gave David three options. David chose the plague option, for he knew that God was more merciful than men. So the angel brought death upon much of Israel, but spared Jerusalem. David was ful of remorse and called down judgement upon himself.

David went up to the temple and made a sacrifice, a sacrifice he insisted on paying for himself despite the urgings of Araunah. The sacrifice stopped the plague. There are obvious allusions here to the sacrifice of Christ.
Why did David insist on taking this census? Maybe at the end of his life he was glorying in his "achievements". However, in judging David God actually had mercy upon him, for it drove David back to his true source of security, God Himself.