After coming back to this thread, I see I must have failed to read the last page before responding! Someone already mentioned the treasure in the field, etc. Ooops.
I thought it would be good to take a look at the complete parable of the virgins:
Matthew 25:1 Then shall the kingdom of heaven be likened unto ten virgins, which took their lamps, and went forth to meet the bridegroom. 2 And five of them were wise, and five were foolish.
3 They that were foolish took their lamps, and took no oil with them: 4 But the wise took oil in their vessels with their lamps. 5 While the bridegroom tarried, they all slumbered and slept. 6 And at midnight there was a cry made, Behold, the bridegroom cometh; go ye out to meet him. 7 Then all those virgins arose, and trimmed their lamps. 8 And the foolish said unto the wise, Give us of your oil; for our lamps are gone out. 9 But the wise answered, saying, Not so; lest there be not enough for us and you: but go ye rather to them that sell, and buy for yourselves. 10 And while they went to buy, the bridegroom came; and they that were ready went in with him to the marriage: and the door was shut.
11 Afterward came also the other virgins, saying, Lord, Lord, open to us. 12 But he answered and said, Verily I say unto you, I know you not. 13 Watch therefore, for ye know neither the day nor the hour wherein the Son of man cometh.
So, we have 10 virgins *like* the kingdom of heaven. It doesn't say they are like believers, but like the kingdom. However, in context, it might mean kingdom = believers. I'll go with that.
Half were wise, half were foolish. (oh my!)
The foolish took lamps - apparently burning, because they went out - but took no oil in a vessel.
The wise took lamps AND oil in a vessel.
They all rested while waiting. The cry came that the bridegroom was coming.
They all got up and trimmed their lamps. The foolish discovered their oil was gone and asked the wise to share.
The wise wanted to be sure their oil would last to the coming and suggested the others go to the source and buy more.
The foolish went, but got back after the bridegroom arrived and shut the door.
They requested to be allowed in.
The bridegroom said, I don't know you - nothing about being late or out of oil.
Jesus made the point that we should always be ready. With what? Knowing him? That was the reason given for exclusion of the foolish, so maybe the oil is not the Spirit at all, but knowing our Lord. The wise made sure they knew him well before they rested. They clearly told the foolish that there was a place they could go to fill their empty lamps. They clearly said they would have to buy the "oil." What's the currency for getting to know our Lord?