Human beings are fallen creatures, the refuse of the earth. Where does the charity of even those who have not been redeemed come from, then? We are refuse, but that does not mean we are not capable of amazing acts. Our rubbishness consists primarily in our love of anything but God, not in our love of acting for the harm of our fellow humans. That common charity comes out because we still know that we were meant to behave like this, but it does not negate our depravity because we still do not do it for the glory of God. Our fallenness consists in our hate of God. Common grace is God's not eradicating us from the face of the earth, but letting us continue to bear his image to the extent that we can. We cannot bear it much, but this is because we hate whatever is of God, not because God has taken anything from us. Perhaps it should be called Common Mercy, rather than Common Grace.
I mentioned when I began this blog that I believe that beginning the search from truth centered on anything but God would be doomed, in the end, to failure. This is not to say that everything found from such a starting point is false, but that it is only true insofar as its center is near the Truth. Some can come closer to it than others, and perhaps no one can quite place him at the very center in practice, but we who say we love him ought to strive to place him at the center of our whole lives.
There is a tug in our very nature to image God to those around us, yet there is also, since the fall, a hate of God which repulses us from being like him, or by any action declaring that he is right. Thus we find people who sway between different sorts of behavior, yet, because they do all from a desire other than for God, it is sinful behavior. Yet we ought to love that they do that which they would do if they did love God, while weeping over their sin in doing it for the wrong reasons. People do amazing things, but too often from sinful desires.