14 David said to Gad, “I am in deep distress. Let us fall into the hands of the Lord, for his mercy is great; but do not let me fall into human hands.”
This is one of my favorite verses. No matter how severe was the punishment from the Lord, it was exeedingly merciful compared to what the hand of man would have accomplished.
So with 70,000 deaths being the wise, merciful option, who can begin to imagine what the enemy would have done?!
It tends to put things into perspective -- how much worse things could be if God's mercy were not an option.
It's a weird little story, though. What got into David that he demanded a direct head count, an obvious big no-no? Was he suddenly channeling his inner data junkie, or what? (Hmmm, thinking.)
In any case, the whole mess caused a very important real estate transaction to take place.
I think the clue to you question is the very first verse in the Chapter. The LORD was wrathful against Israel, and then used David to punish them. We know what the big sin of Israel was...running after the false gods of the Land they were inhabiting. Even David’s assistant knew that “Counting the Fighting Men” was a sin against Faith in God’s Provision and Guidance, and David soon realizes that HE is responsible for the sin of his people, since he is the Shepherd, and should have known better.
But, just think. If that whole debacle hadn’t occurred, David would never have seen the Angel up on the Temple Mount, and Solomon would never have built his Temple on that precise spot.