Newton's first law states that an object will keep doing what it is doing if left alone, in other words - The natural state of an object is static - unchanging - motion.
Newton's second law clarifies the first. Acceleration, or any change in motion, is an unnatural state for an arbitrary object left to its laurels, however it is a state that clearly exists all around us. Newton defines the "thing" that forces an object to change its state of being - a force.
In this most rigorous sense, a force is defined to be that which causes a change in motion.
The observation of a change in momentum necessitates that there is some force driving that change, so in this sense the two are equivalent (there is an equals sign there after all) - wherever you see a (net) force you will see an acceleration, wherever you see an acceleration you will find a force responsible for it. However, going back to the first law, acceleration is a change in the (kinetic) state of an object, an objects natural tendency is to statically maintain its state. The observation of an unnatural state of being would logically imply that there is a cause.
Intuitively it seems unnatural that accelerations would happen spontaneously and that the universe will invent a force just to balance the books if you will.