What it means for God to be impassible

While God and rocks may both be impassible, they are so for polar
opposite reasons. A rock is impassible because, being an inert
impersonal object, it lacks all that pertains to love. God is
impassible because His love is perfectly in act (“God is love”) and no
further self-constituting act could make Him more loving. God is
absolutely impassible because He is absolutely passionate in His love.
Thus creatures, and particularly human beings, through the act of
creation are immediately and intimately related to God as He exists in
His perfectly actualized love.

Thomas Weinandy, O.F.M. Cap., “Does God Suffer?“, First Things magazine, November 2001.