Samuel The last chapter

David just told Joab and his commanders to go out and find out how many fighting men were in Judah and Israel.

8 So when they had gone through all the land, they came to Jerusalem at the end of nine months and twenty days. 9 Then Joab gave the sum of the number of the people to the king. And there were in Israel eight hundred thousand valiant men who drew the sword, and the men of Judah were five hundred thousand men. 10 And David’s heart condemned him after he had numbered the people. So David said to the LORD, “I have sinned greatly in what I have done; but now, I pray, O LORD, take away the iniquity of Your servant, for I have done very foolishly.”

I do not understand why David doing this was wrong I am going to talk to Dad about this and then I will type it out. But then a prophet came to David and gave him three options of how he would be punished, and David chose a 3 day plague That killed seventy thousand people. O my, I hope Never to do such a thing as whatever David did.