There is a simple explanation.
Imagine yourself working for a corporation, large or small (Hopefully you do have a job so this would immediately strike a cord).
When you are part of a corporation or organization, you are essentially a representative of the company, You are responsible for providing good service, whether it be customer interaction or simply giving a customer an item though you have not met them in person or spoken on the phone.
Customers will also judge your decorum, your knowledge and everything, even your body language. So how you act is very important, as it would leave an impact on them, either good or bad.
If you provide a satisfactory to outstanding service, the people are going to return to the company and recommend it to others, but the opposite will happen if poor service is provided, causing potential customers to head elsewhere for their goods.
If something goes wrong because of you, it is often the manager and the owner who get held accountable for YOUR mistake, which doesn't reflect well on the company when it goes wrong.
You as an employee for a company are the representative of the executives in charge and thus an audience's perception of the employee is going to be placed on the employer in question. This is a tremendous problem and repentance has to be undertaken to ensure this doesn't happen again. It won't change the customer's perception of the company but you will at least learn from the mistake you made and not to repeat it.
Likewise, you see why the world is quick to judge Christianity and ultimately Jesus when a Christian slips up. I am not saying this happens ALL the time but it is common.
Why is Jesus blamed for the terrible suffering of Jews, even though he never hated his people but had compassion for them? Why are homosexuals blaming religion for the persecution of them, when Christians should have had compassion on them and brought them to repentance?
How a Christian acts toward an unbeliever may either enhance or damage the witness of Jesus Christ in their lives, the latter of which causes unbelievers to see Jesus as a moral monster. of course sinful man sees YHWH and the Bible as reprehensible anyway but you catch my drift? We have to ensure there isn't a failure to let our light shine before men so that they may say our good works and glorify our Father in heaven (Matthew 5:16). Plus as Jesus pointed out "If salt looses it's saltiness, how shall it's saltiness be restored?" It is rendered garbage to be thrown away (Mark 9:50, Matthew 5:13 and Luke 14:34).
Remember that how we live in the Christian life, an unbeliever can see who is and who isn't in some cases, but there are other cases where Christianity or Jesus is blamed for an atrocity. It doesn't reflect well on the employer and his company when the employee behaves badly, so keep that in mind with Jesus and his company and do not do him disservice.
May we all be loyal to him and may he forgive us our faults and trespasses.