First, they have to be shaped. You can’t throw a handful of snow very far or very accurately. Instead, you must shape it into some semblance of a ball to have any prospects of reaching the target.
The same is true with us. God has to the scrape off things in our lives that make us unstable projectiles and form us into new shapes to put us on target. We have to yield to His shaping to get where He wants us to go; otherwise we fall short of the mark.
Second, good snowballs must be squeezed. A loosely formed snowball has little impact because it’s mostly air. But when pressure is applied, that air is removed and the same amount of snow will make a much greater impression. That increased impact can only come through pressure.
Once again, the same is true of us. God has to let us go through some tough situations to squeeze the fluff from our lives. It’s not easy, but it must be done if we are to have the impact He wants.