A foolish man also knows the truth. He knows that Christ is coming again. He knows also that he ought to pay attention to this truth and that he ought to live a life in conformity with it. But he pays no attention. He lives as if Christ will never come and as if this world will go on forever.
Foolishness is always principally rooted in unbelief.
The wise virgins took oil in their lamps while the foolish virgins did not. In general it seems as if the oil in the parable is simply a picture of preparedness. Those with oil were prepared for Christ's coming, while those without oil were not. This preparedness is basically the watchfulness of the church as she is called to live in daily anticipation of Christ's return. Five of the virgins were only virgins outwardly.