It makes a big difference if the wind is blowing 30 miles per hour from the North, from the South, from the East, from the West, or from the Southeast, etc.
In order to fly the plane in the direction that he actually wants to go, the pilot needs to handle every possible wind direction in a different way.
If he only knows that the air he's in is moving over the ground at 30 miles per hour, he would have no way to make the required correction, and the airplane would get blown way off-course.
Air speed is how fast you are peddling over the ground, wind speed is how fast the wind is blowing above the ground.Depending on the correlation between the two with direction thrown the pilot knows what sort of resistance he is flying against.
