What fuel is to a car, the Holy Spirit is to the believer.
He energizes us to stay the course. He motivates us in spite of the obstacles. He keeps us going when the road gets rough.
It is the Spirit who comforts us in our distress, who calms us in times of calamity, who becomes our companion in loneliness and grief, who spurs our “intuition” into action, who fills our minds with discernment when we are uneasy about a certain decision.
In short, He is our spiritual fuel. When we attempt to operate without Him or to use some substitute fuel, all systems grind to a halt.