(6) But we are all like an unclean thing,
And all our righteousnesses are like filthy rags;
We all fade as a leaf,
And our iniquities, like the wind,
Have taken us away.
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This verse certainly puts human righteousness in a bad light compared to what is truly good. GodHimself is making this judgment, and He makes His comparison against His own righteousness. Measured like this, all of what we do that we consider our righteousness is filthy! Yet, human nature loves to compare itself with others less than God, and by such means, we come out smelling like a rose. Human nature tends to isolate one aspect of another's personality or character and conclude that in comparison, the self is pretty good.
However, the problem is that this is not a comparison our Judge, God, finds acceptable. Human nature likes to consider itself good. That is not too hard to do because, as judged by human standards, the overwhelming majority of humankind—those ordinary people who are not out murdering their neighbor, robbing the local food mart, or dealing drugs—is reasonably good. Human nature tends to judge itself against such, so the standards are not exceedingly high.
Notice what Jesus says to people of this sort: "If you then, being evil, know how to give good gifts to your children, how much more will your Father who is in heaven give good things to those who ask Him!" (Matthew 7:11). Notice that Jesus, God in the flesh, judges these people to be evil! Nothing in the context indicates that they were anything but run-of-the-mill citizens of the area. They were not Al Capone and his mafia mob!
This is in perfect alignment with Isaiah 64:6 and Matthew 19:17, where Jesus says, "No one is good but One, that is, God." He judges them to be evil, even though what they were doing was essentially a good work, giving good gifts to their children. We can see that some element must be missing from the acts of human nature apart from God that He finds unacceptable.
We are self-righteous, but we need to become God-righteous. This is why none of our works can earn justification. All of our acts before conversion are tainted by the fact that they are constantly under the influence of Satan and this world, even though some of them are even "good."
— John W. Ritenbaugh