Answer:
The reason one must apply a force to a box in order for the box to move is to overcome the friction generated by the box against the plane the box is sitting.
The box at rest has zero friction against the surface on which it sits. Once a force is applied, a box's movement is resisted by the friction created from contact with the surface.
In order for the box to move, one must generate more force than is being generated by the friction of the surface onto the box, allowing the box to move.
Cheers.