‘How much more will your Father in heaven give the Holy Spirit to those who ask him!’ Luke 11:13b
Jesus has spoken this parable, referring to the very last moments before His coming back to earth. At the time of His return the Kingdom, which is already revealed in the hearts of the believers - for Jesus said that His kingdom is in our midst (Luke 17:21) - will be comparable with the situation described here.
All ten virgins waited for the bridegroom to celebrate his joyful entry into the house of the bride. This was a festive event that usually involved the whole village. Now, of course, there are always people willing to party; some go from one party to another. They offer hasty congratulations and cast eager eyes on food and drink. These are people, who attend parties for the sake of partying: they go only for their own fun. But, fortunately, at every party there are also people, who attend to celebrate with the person in whose honour the party is given.
This, I feel, illustrates the difference between the five wise virgins and the five foolish virgins more clearly. The five foolish virgins came for the fun, to get what they could get out of it. They had brought their lamps, but they lacked the least bit of care. Neither were they interested at all in how they could possibly contribute to the party. The meaning of the feast escaped them, because they obviously had no relationship with either the bride or the groom. They were there for themselves and not for the sake of the two people celebrating their wedding.
Therefore the oil in this story is surely a symbol of the Holy Spirit. For without the Holy Spirit we just want to be Christians to be blessed, and not for the sake of Him, Who gives the blessing.