Paul realized to the marrow in his bones that he was sinful. But he wanted to do what is good. He had a will of steel that kept him from committing a great many sins, but he still sinned, and he hated it every time he did. So, he was grieved deeply that he could not perform what God required of him because of that deep-set sin within human nature. Because we are so selfish, we allow human nature to lead us around by our noses and indulge ourselves when we should be sacrificing ourselves.
This sorrow is what Jesus is advocating when He says, "Blessed are those who mourn" (Matthew 5:4). He wants the kind of sorrow that is grieved to our innermost being that we are not like Him, that we are full of sin, that we cannot ever seem to move beyond our carnality. We see it cropping up so often, and we hate ourselves for it. We grieve because of our weakness.
This sorrow is always appropriate and applicable in our walk with God. It is a deep conviction that we are unworthy, and we are upset about it. We grieve that we cannot match the perfection of Jesus Christ. We always have miles to go, but Jesus also promises comfort at the end of that hard road.
