I will also make you a light for the Gentiles, that you may bring my salvation to the ends of the earth (Isaiah 49:6)
I believe that today you can change "Gentiles" to "non-believers" and realize that this scripture suddenly applies to your life. God has made us a light to shine into the lives of everyone with whom you associate.
The problem, I believe, is that most of us (myself included) don't recognize this and/or don't walk in it. Maybe it's a low feeling of self-worth, that no one would look to us to see God's salvation, or maybe it's because we're still holding on to an area of sin in our lives and we don't want anyone to notice.
But you know what, the light is there no matter what. If people know you are Christian, there is a spotlight shining on you. It's a harsh light sometimes, and it will point out all of your flaws. This light is not necessarily the light from God that Isaiah was talking about. But it's not all bad either. Sometimes we need to realize that we are going to be in the spotlight around people who know we believe in Jesus Christ. They will be examining us to see what makes us who we are, and yes even looking for those cracks in the foundation. Because people who resist the Truth will want to make you out to be a liar.
And when we are hiding in shame or sin, this spotlight is worse than the "ugly lights" that turn on when a bar hits closing time. We can try to pull a covering over ourselves to hide our shame or our dark thoughts and actions, but the world will cast it away and point and stare, and the more you attempt to live in the shadows, the more your actions will be brought to light.
If you accept the Holy Spirit into your entire being, however, you will find that the light around you is actually a light within you. It is the living Spirit of God exuding from your very pores. Because as you open yourself up to God and surrender your own identity to His, the pure and true light of Christ will shine from within you. It will show in your eyes, in your words, in your actions, in your very bearing. And you will find that this light, even though it is softer and much more gentle, completely obliterates the world's spotlight. Because you are welcoming the scrutiny. "Seek," you will tell the people around you. "look into my life and see the joy that I have which is from Christ."
It is this light which will shine through the darkeness of the world. And if you have accepted Christ as your Savior, it is this light which resides in you, right this very moment. All you need to do is surrender to it. Recognize that people will be looking at you anyway with their own judgements and presuppositions, but the more you open yourself to God, the more light will shine through, yes even through your flaws, so that they may glorify God that much more.
You are a light to the world. Shine on, baby, shine on.