They did not qualify to go in the procession with a burning lamp. It is a Jewish wedding custom. They had to be ready to join right in with a burning lamp. The Groom comes with his followers and they have to join right in, no time to go get more oil and come back the procession is already moving and they have to step into a moving parade, it will not stop for them and wait for them, So what's the lesson from a custom familiar to the hearers who heard this parable SPOKEN not written? There was an immediate "ah Ha, I get it" What do you think it was? The oil being the Holy Spirit? I doubt that. The main "ah Ha" Would naturally be, "you better do what you need to do to be ready when the Lord comes" And of course that lesson gets repeated in other parables. And taught doctrinally in the New Testament epistles. \
Afterward came also the other virgins, saying, Lord, Lord, open to us.
12But he answered and said, Verily I say unto you, I know you not.
13Watch therefore, for ye know neither the day nor the hour wherein the Son of man cometh.
So that was the lesson
Watch therefore, for ye know neither the day nor the hour wherein the Son of man cometh. But the parable drove it home and called for a response. What will you now do to make sure that you are watching?
If you say, I will get extra oil and then you decide that the oil is the Holy Spirit, how exactly would you get extra oil? If you say I will pray always, this will supply the grace of the Holy Spirit in my life, then you are on the right track but you could teach something unsound if you try to teach that your prayer gives you more Holy Spirit than your brother who does not pray as many hours as you do. So a definition of how to have extra oil is going to produce all sorts of interpretations and none of them are necessary because what the oil represents is not critical to the lesson.
Watching is.