Yesterday I went to the doctor. It was nothing serious, just a check up. I walked in, the nurse had me step on the scale, checked by height, took me back to the examination room, took my temperature, my pulse, and my blood pressure. It was a check. 
This past Sunday we confessed a part of the Small Catechism that deals with checking ourselves:
What should a person do if he or she does not feel a need for forgiveness?
To such a person no better advice can be given than this: first, he should touch his body to see if he still has flesh and blood. Then he should believe what the Scriptures say of it in Galatians 5 and Romans 7. Second, he should look around to see whether he is still in the world, and remember that there will be no lack of sin and trouble, as the Scriptures say in John 15 and 16 and in First John 2 and 5.
I’ve always appreciated this “vital sign” check from Luther (or I suppose you could say it’s a check of the opposite of vitality). If you don’t feel like you need forgiveness, check to see if you have a body. Have a body? Check. You have sin. That’s the effect of original sin. We’re all born with a mutation, the mutation of original sin, it’s going to be there. Likewise, everyone else is born with this mutation as long as we’re still in the world. It’s like checking our pulse. Paul tells us that all have sinned and fall short of the glory of God.
But here is the crazy thing. One day when Christ returns in the Resurrection, we won’t have sin anymore. It’ll be like waking up without a pulse, without a temperature, without blood pressure (although I’ll argue that we will probably have those things in perfection). Waking up one day without sin is going to be crazy. On that day, we can follow Luther’s advice and feel our bodies and not feel a need for forgiveness. On that day, we will look around and not see sin and trouble, but see righteousness and peace.
I’m looking forward to that check up.