Have nothing to do with the fruitless deeds of darkness, but rather expose them. It is shameful even to mention what the disobedient do in secret. But everything exposed by the light becomes visible – and everything that is illuminated becomes a light.
Wesley says of verse 11, "to avoid is not enough." Paul warns his friends to steer clear of what will hurt them and seduce them into old-self behaviour (2 Corinthians 6:14-17), but amidst the mess we have a job to do. And it is a job in which we imitate our saviour. Jesus always knew that his light-ness would cause problems: dark doesn't like light therefore we should expect hostility and even hatred as we live our counter-cultural life. (John 3:19-20; 1 Corinthians 4:5). Ultimate exposure, reproof, conviction is the work of the Spirit, but we are not to shirk responsibility: we must join Him in showing up what isn't Kingdom.
The language here is of making visible things for what they really are, a bringing into the cold light of day that which is shadowed and shady, a letting people know that certain things are not ok: that difficult conversation explaining to an 11 year old why it isn't ok to call his Sunday School teacher a 'bitch'; a gentle word about someone's Facebook use; acting as a peacekeeper amongst those who would rather cling to grudges and fester in dispute. This is risky business: as the minibeasts who make their life under a stone flee from the hand of a child who turns over their dwelling place, so we will encounter painful reactions to our shininess. Some things don't want to be exposed. Some things long to be hidden. Some things will always flee from the light. And yet this is not just the business of dark-destroying but light-making: an 11 year old who knows the damage caused by awful words might just become a little bit shiny himself. This is not a call to judgement or condemnation, but a firm bringing back from the brink (James 1:19-20); gentle restoration from a place of love (Galatians 6:1).
Don't hide your light; let it rub off on someone today.