Calvin W. Allison said this quote

The wind stirs through the trees, it moves the leaves, and it sways the branches—and yet it is unseen. The sound of it is detected, the effect of it is noticed, and yet it itself is unseen. In a way that is similar: the Spirit stirs in the heart, it moves emotions, it sways the mind, and by doing so causes a physical response to occur that defies human logic, and transcends perception.