When I think about will and action, I often think about full speed ahead physical movement. The CHARIOT is most definitely about will and action, but notice the lack of physical movement in this card. The Chariot almost looks fixed like some of the food carts I see when I go to Portland. They have wheels and are mobile, but most are actually stationary for a good chunk of time. They have everything they need to function, and they operate from one particular place for a while until their rent runs out, or they decide to move on.
The Chariot can go anywhere and be successful. S/he has everything s/he needs within hir including skills, confidence, and faith that s/he will be taken care of because s/he is always ready to take necessary action to collaborate with the Universe.
In this version of the card, the sphinxes are at rest and the driver is not holding onto reigns. In fact, there are no reigns visible in the card. This is because the driver has learned how to control the sphinxes with hir will and intent. Depending on the reading, the sphinxes might represent the conscious and the subconscious, the active and passive, opposing thoughts or desires, animal and human nature, or even what some might call the feminine and masculine parts of ourselves.
The Charioteer is no longer driven by hir mind or the ways that s/he was domesticated and taught to be. S/he drives this Chariot using hir mind and hir will as tools.
The driver has basically learned how to live and act from a place of choice rather than reaction. Living from choice always requires a strong will, and the ability to be still or move forward depending on what is needed.