"Let us not therefore judge one another any more: but judge ye this rather, that no man put a stumblingblock in his brother's way, or an occasion of falling." (ASV)
Have you ever caused someone else to sin? Most of us don't ever think about this, but it is something we are called to watch out for. Maybe your groans of disapproval at work set the stage for others to badmouth the boss. Maybe the skin-tight shirt you wore last weekend caused people to look at you in lust. Maybe you were just in a bad mood yesterday, and passed your irritability on to those around you.
It's important that we as Christians not only look after our own spiritual walk, but also those of our brothers and sisters. We are supposed to encourage them toward right ways and right decisions, not be the thing that inspires sin in their lives. We are to care for them as our own family, and help them to walk closer with God, just as they encourage us in our own walk.
If you have a friend who struggles with alcoholism, you wouldn't offer him or her a drink. Sin is the same kind of addiction in our lives. It's deep roots go all the way to our very core where it has hold of us. Just like an alcoholic must be vigilant against drunkenness all his life, we must struggle against our sinful natures. Those who allow a drug addict access to drugs are called enablers. This can be either active or passive, but either way it's no less destructive in the addict's life. So too can we become sin enablers by placing our friends and fellow Christians into situations where we know they may be tempted. Whether we intended for them to fall into sin or not, the result may be just the same.