I've heard the oil signifies the Holy Spirit.. but why would the Holy Spirit not indwell a born again believer?
What is your understanding?
Scripture is it's own Interpreter:
See to it, brothers, that none of you has a wicked heart of unbelief that turns away from the living God.
But exhort one another daily, as long as it is called today, so that none of you may be
hardened by sin’s deceitfulness.
We have come to share in Christ if we hold firmly to the end the assurance we had at first.
As it has been said:
“Today, if you hear His voice, do not harden your hearts, as you did in the rebellion.”
For who were the ones who heard and rebelled? Were they not all those Moses led out of Egypt?
And with whom was God angry for forty years?
Was it not with those who sinned, whose bodies fell in the wilderness?
And to whom did He swear that they would never enter His rest?
Was it not to those who disobeyed?
So we see that it was because of their unbelief that they were unable to enter.
Scripture does not lie - but men do