All of us have become like one who is unclean, and all our righteous acts are like filthy rags; we all shrivel up like a leaf, and like the wind our sins sweep us away. Isaiah 64: 6
Our righteousness is but filthy rags before a holy God. The Apostle Paul wrote about righteousness as well and the language is even stronger:
What shall we conclude then? Are we any better? Not at all! We have already made the charge that Jews and Gentiles alike are all under sin. As it is written: "There is no one righteous, not even one; there is no one who understands, no one who seeks God. All have turned away, they have together become worthless; there is no one who does good, not even one." "Their throats are open graves; their tongues practice deceit." "The poison of vipers is on their lips." "Their mouths are full of cursing and bitterness." "Their feet are swift to shed blood; ruin and misery mark their ways, and the way of peace they do not know." "There is no fear of God before their eyes." Romans 3: 9-18
So what must we conclude today? Are we any better than those in the world; the Gentiles of today? No, because we are all alike under sin. The difference is that we have been saved by grace. It is that grace that we are supposed to show the world that still walks in darkness, not condemnation nor self-righteousness. It is not mere words we are to show but our deeds. It is through whom we are, that others will want what we have not by persuasion. It is no wonder that the remainder of the teaching from the Sermon on the Mount shows Jesus telling us how we ought to behave, not speak. But Jesus cut even deeper than that. He did not only teach against the behavior, but the root sin behind the behavior. Because the world will see through the hypocrisy of man because hypocrisy is a product of the darkness they are all too familiar with. Going in order after the teachings on salt and light and fulfillment of the law we see the following teachings from our Lord and Savior:
1) We should not murder. Going deeper though Jesus teaches that we also should not be angry nor hold things against one another. The world does not need to see angry Christians telling them of the virtues of Christ.
2) We should not commit adultery. Going deeper though Jesus teaches we should not look upon people with lust in our hearts. The world does not need to see Christians professing morality in the midst of their own moral failings.
3) We should not divorce except for unfaithfulness. Going deeper though Jesus teaches that unwarranted divorce is actually adultery. The world does not need to see Christians decrying the problems in the world with the sanctity of marriage and the family unit amidst divorce rates comparable to the world.
4) Oaths Jesus teaches that our word must stand for something. Another teaching against hypocrisy.