God would not rub so hard

(Thomas Brooks, "The Privy Key of Heaven" 1665)

"I will turn My hand against you and will burn away
your dross completely; I will remove all your impurities."
     Isaiah 1:25

Afflictions cleanse and purge away the dross, the filth,
and the scum of the Christian.

All the harm the fire did to the three children, or rather
the three champions--was to burn off their cords. Our
lusts are cords of vanity, but the fire of affliction shall
burn them up. Sharp afflictions are a fire--to purge out
our dross, and to make our graces shine; they are a
potion--to carry away ill humours; they are cold frosts
--to destroy the vermin; they are a tempestuous sea--
to purge the wine from its dregs; they are a sharp
corrosive--to eat out the dead flesh.

Afflictions are compared to washing--which takes away
the filth of the soul, as water does the filth of the body.
God would not rub so hard, were it not to fetch out
the dirt and spots that are in His people's hearts.