I'm going to attempt a highly unusual and possibly controversial metaphor, so let's ignore the connotations associated with either entity and try to look at them as objective ideas.
A passive Christian is like a passive smoker. You grew up in a family of smokers and never really lit the cigarette yourself, but was always surrounded by the fumes. You breathe in the smoke of others. You do not have the first-hand experience but you take in what the others do all the same, and you call yourself a smoker, too, although that's technically not fully true. Once you realise that you aren't a real smoker, that you've only been living on the stuff of others, glimpses of their own real smoking experiences, you have three choices. You can shrug and leave it as it is, continuing to be a passive smoker, perhaps still calling yourself "a smoker", or just acknowledging that you don't really know what it's like first-hand. You can decide that you want to remove yourself from the association with others' identity, remove yourself from your delusion and the house. Or you can decide to experience it for yourself, light your own cigarette, let your lungs fill with your own.