Paul comes back to the beginning of mankind as he did in 2:1-3. The beginning is the same but it is the greatest of starting places because it makes the gospel so wondrous news! That beginning? That every person is darkness, not surrounded by or in, but at his very nature he is darkness with no light at all.
However, following our dismal beginning he follows it with who we now are: light. Again, we are not in or surrounded by light, but we are light. How so? Jesus' blood being shed at the cross that covered my sin. He has made me light! Because I have been given such a glorious title, I must live as the title says. I am light, thus I live as a child of it. In the same way, I could not be a professional chef and never cook anything following the designation. Paul helps us with what living this light of life looks like. He gives 3 fruits (or traits) goodness, righteousness, and truth. Everything Christians due must uproot from these three fruits. Paul has been broad until this point and he continues so here in that Christians lives are going to look different in expression, but the principle fruit remains the same.
Verse 10 is one of the clearest verses of daily sanctification. Here, Paul's aim is to get the believer to think about his life and examine everything he does to see if it pleases God. This is, both, an internal and external examination. Again, Christ does not save us so we can sit pat. No! He saves us that we might live to the glory of His name. Bearing these fruits and examining the outworkings of our lives to the pleasing of God is what its all about.
