I love this verse. I love the image of light and darkness here. Throughout Scripture, light is associated with Jesus- that which is holy, darkness is associated with Satan and our flesh- that which is evil. When you accept Jesus as your Savior, the Spirit of God lives within you. He convicts you of sin- revealing to you the darkness in your life. Some of the darkness you might be completely aware of- other things are less noticeable to you- you didn't realize you only had a dim light on and weren't able to see clearly. Other things the Spirit reveals to you are the dark corners in your life- the ones you know about- but choose to forget about. The darkness that you don't want anyone to know about. The Holy Spirit will shine His light not only in the dim areas, but the pitch black areas. But when He shines His light into those places, you will be purified, as long as you don't try to turn the Light out. The closer you get to Jesus, the less darkness you have. In fact, a follower of Jesus that chooses to live a repentant life will not have any dark, hidden corners in their life. They choose instead to confess their sin, have accountability partners, and allow the Light to penetrate every area of their life- so that nothing is hidden. Because we are flesh, we will always be sinful- we can't be perfect- but our sin doesn't have to be hidden from others. James 5:16 says, "Confess your sin to one another, and pray for one another, that you may be healed."
Some areas of darkness for me have been clear- others not so much- and I have had the dark corners I didn't want anyone to know about. For instance, some darkness for me that was noticeable was my drinking and drug habits. When I accepted Jesus, the Holy Spirit shone His light there and delivered me from that sin. The darkness that was revealed to me by His bright light was the selfishness, greed, and approval for others in my life. I didn't see this sin right away, it took awhile before I was willing to let the light in that area. My dark corners of life were my addiction to pornography and my undisciplined, ungodly spending habits. The porn speaks for itself, but my spending habits were just uncontrolled. It wasn't that I was going on shopping sprees and swiping the credit card, but it was being negligent of telling my husband all that I bought. It was giving up controlling the budget, my credit card and coming clean about my habits. I hadn't gotten us into debt shopping, it was the principal that I didn't want to tell my husband the whole truth, because I knew I had spent money on things that were foolish.
These are only a few examples, trust me, I have many other things in my life that the Spirit is revealing to me with His light, through His grace and love for me.
Let the Light shine!