Franklin needed something to get close enough to the clouds to attract the lightning. He couldn't get up there since Philadelphia didn't have any hills or tall buildings. He did have a silk handkerchief, a couple of sticks and some string, so instead of getting himself up near the lightning, he flew a kite up to it. And it worked! Franklin and a few other scientists in Europe (who did their own experiments) proved that lightning and electricity were the same thing.
But that wasn't enough for Franklin. He believed that this knowledge should be used for practical purposes.