What does 2 Samuel 24:11 mean?

So when they had gone back and forth through all the land, they came to Jerusalem at the end of nine months and twenty days.

Joab gave up the sum of the counting 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.

David’s heart struck him after he had counted the people. David said to Yahweh, “I have sinned greatly in that which I have done. But now, Yahweh, put away, I beg you, the iniquity of your servant; for I have done very foolishly.”

“Go and speak to David, ‘Yahweh says, “I offer you three things. Choose one of them, that I may do it to you.”’”

So Gad came to David, and told him, and said to him, “Shall seven years of famine come to you in your land? Or will you flee three months before your foes while they pursue you? Or shall there be three days’ pestilence in your land? Now answer, and consider what answer I shall return to him who sent me.”

David said to Gad, “I am in distress. Let us fall now into Yahweh’s hand; for his mercies are great. Let me not fall into man’s hand.”