It’s an interesting negotiation if you think about it. God gives us a command and we break it. We, justly, should be disciplined. However, our bargaining position is that if God doesn’t discipline us or, even more boldly, also removes the natural consequences of our sin, we won’t break His command again.
That’s not a bargain at all!
It’s really more of a threat, isn’t it? It implies that if God doesn’t save us that we will keep breaking His commands, all the more deserving those consequences.
David shows us a different way of asking God for mercy.
Rather than trying to convince God to show mercy because of something he (David) had done or some characteristic he (David) embodied, David appeals to God’s own characteristics and actions.