The term “instrumental nature” is based on the idea that we are not so much clever animals that may or may not have a soul, but that we are souls who may or may not have a body and mind.
In other words, in our essence we are a conscious, eternal and immutable Self; in our naïve, unregenerate state we tend to identify with our body-mind; but as we develop we can learn to identify with our eternal Self, and then use our body-mind as an instrument to manifest ourselves in the socio-physical world.