What are you rich in? Is it humor? Or relationships? Sarcasm?
Truth is - we're probably rich in a few things to at least some degree.
But this verse declares that God is rich in mercy. What a thing to have an abundance of! And - He's rich in it towards us. And He's not rich in mercy towards us because He's obligated, or because He's so much mercy He's got to figure out how to get rid of it before His taxes are due. Nope. It costs Him dearly to be so rich and generous towards us - but He's happy to be so - because He loves us so much and this is His favorite way to show it.
And the effect of this wonderfully love-fueled abundance? Nothing other than bringing us back to life from the dead through it - but distinctly different than before. Before it was just us - kicking around, making trouble, and winding up needing mercy. But now - we are made alive again with Christ. As radical a change of existence as any one can imagine or contemplate. To be alive with Christ means that every single thing we do from now on - is purposeful, potentially redemptive, and done with essentially God's own two hands and feet.
To be alive with Christ in this world - is about one thousands times more outrageously awesome than being passed the ball by Michael Jordan in the dead last second of a championship game - when you're unguarded and right next to the basket - all set up to make your signature shot. Michael could shoot the three pointer without you - but instead He gives you the shot. God could do this with someone else - or even on His own - but He's passed us the shot.