Matthew 25:2-4 ESV
Five of them were foolish, and five were wise. For when the foolish took their lamps, they took no oil with them, but the wise took flasks of oil with their lamps.
The oil of faith and obedience is necessary to make one wise. The fool in Scripture typically is the person without God. A person without the presence of the Spirit in their life is as a person without God, for God is Spirit.
It is the Spirit which enables fruit in our lives. Believing is more than a thought. It is in being the light. For the light to be present, the oil of the Spirit is necessary.
Now I want to remind you, although you once fully knew it, that Jesus, who saved a people out of the land of Egypt, afterward destroyed those who did not believe.