One group made sure they had enough oil. The other group trusted that what they had was sufficient. Maybe they believed in a form of eternal security. Maybe they felt they didn’t have to be diligent in the responsibilities given to them, and that they were guaranteed a place at the wedding regardless of what they did or didn’t do.
This parable is unsettling because there are no obviously bad actors. There are no blatant sins here. The ones designated as foolish are not depicted as wicked, defiant, incorrigible, or lawless. They are simply unconcerned with being personally prepared. That is what makes them foolish. They had the same opportunities as the wise to build up a reserve of oil, but their choices continually took them in other directions, perhaps because they believed they were secure regardless. They assumed it would work out. They did not realize until too late that their ending would be the same as those practicing lawlessness while prophesying and doing wonders: The Lord tells them, “I do not know you.”
There are countless events or circumstances that God does not desire, and which He warns against and may even hate, but which He allows to play out. God’s silence, or the fact that He did not intervene to stop something, must not be taken as His approval (Psalm 50:21). In this parable, God allowed half to act wisely and half to act foolishly, but the foolish ones had no grounds to blame God for their lack of preparation.