In Parshat Emor, God tells the Jewish people:
"You shall not desecrate My Holy Name, rather I should be sanctified among the Children of Israel." (Leviticus 22:32)
The primary privilege and responsibility of every Jew is to create positive PR for God and Torah. Certain mitzvot clearly achieve this, like Brit Milah - circumcision. Why would we perform non-medical surgery on a helpless baby - and on such a sensitive part of the body? The only possible motivation is that God said so! By doing so, I increase the respect for God in the world, which is the essence of sanctifying God's Name.
Every aspect of our behavior can foster this. I once asked a woman what led her to make a commitment to Torah observance. 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 is demoralizing because there is a feeling that if the Jewish people - the "Light unto the Nations" - are corrupt, then what hope is there for the rest of us?
Every great opportunity presents with it a great responsibility. God's good Name is on the line. And it's up to us.