interesting parable. They were all believers, but some knew how to get ready and to stay ready. As with the church today. Many profess Christ, but have not kept themselves ready; prepared. And these then try to "borrow" faith and steadfastness from other belivers who have made it their goal to "keep ready" because no one knows when He will come for the bride. They never do the work themselves of preparation, but expect that they can survive off the prepared others. they latch on to strong believers like leeches.
And like leeches, we have to shoo them off, so that we ourselves do not get swallowed up and have no oil for ourselves. To some, this doesn't sound very Christian. After all, we are called to share and to give. But they forget that it is each is responsible to "work out your own salvation with fear and trembling." God help us to see that each individual Christian needs to prepare for themselves.