Eroding Mountains

Don't say, "Since speech is merely modulation of air, it is of no consequence." Just consider that G-d forms mountains - a very concrete and solid entity - and creates the wind - an ethereal and intangible phenomenon. Yet we see that the wind has the power to erode a mighty mountain. The phenomenon of erosion should tell you that although speech may be ethereal and fleeting, it wields enormous power.

(Rebbe Yisroel of Rizhin)