Kiddush Hashem

The Holocaust produced many heroic deeds of Jews standing loyal to God, in the face of the most impossible conditions.
A beautiful story illustrates this idea (from "Stories of the Holocaust," by Yaffa Eliach):
One of the forced laborers in the camps relates that one day he heard frightening cries of anguish the likes of which he had never heard before. Later he learned that on that very day a selection had been made - of infants to be sent to the ovens. We continued working, tears rolling down our faces, and suddenly I hear the voice of a Jewish woman: "Give me a knife."
I thought she wanted to take her own life. I said to her, "Why are you hurrying so quickly to the world of truth..." All of a sudden the German soldier called out, "Dog, what did you say to the woman?"
"She requested a pocketknife and I explained to her that it was prohibited to commit suicide."
The woman looked at the German with inflamed eyes, and stared spellbound at his coat pocket where she saw the shape of his pocketknife. "Give it to me," she requested. She bent down and picked up a package of old rags. Hidden among them, on a pillow as white as snow, lay a tender infant. The woman took the pocketknife, pronounced the blessing - and circumcised the child. "Master of the Universe," she cried, "You gave me a healthy child, I return him to You a worthy Jew."

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Every aspect of our behavior can foster a Kiddush Hashem. I asked a woman who recently became observant what led her to make such a commitment. She said that when her 10-year-old niece became observant, the girl transformed from being a spoiled brat, into a model of kindness and compassion. The woman said, "If this is the effect that Torah has on a person, then I want it, too!"
On the converse, a Jew acting in a despicable manner is a desecration of God's Name. Which is why we are so bothered when a Jew cheats in business. Besides violating the Torah prohibition of stealing, the additional tragedy is that people will say, "If this is the effect that Torah has, then I don't want any part of it." It distances people from connecting to God.
Even further, such behavior demoralizes society, because there is a feeling that if Jews - the "guardians of morality" - are corrupt, then what hope is there for the rest of us?