Here's why:

* Acceleration is the rate of change of velocity. Velocity is a vector quantity, meaning it has both magnitude (speed) and direction.

* If a body is at rest, its velocity is zero. This means it has no speed and is not moving in any direction.

* For a body to have acceleration, its velocity must be changing. Since a body at rest has a velocity of zero, its velocity cannot be changing. Therefore, it cannot have acceleration.

However, it is important to note:

* A body at rest can be about to accelerate. For example, a car at a red light is at rest, but when the light turns green, it will start accelerating.

* A body at rest can be experiencing net zero acceleration. This means it may have multiple forces acting on it, but they are balanced, resulting in no change in velocity.

Let me know if you have any other physics questions!