I ran across the same description of a character in one of my favorite books - The Hammer of God by Bo Giertz. The protagonist, Savonius, is struggling with the idea of faith alone in Jesus for salvation. God sends an older, fellow pastor his way.
Now God had sent him another helper. But the help was the same. He felt as if he had stumbled against something eternal and unmovable, something at the innermost corse of existence, something that was at the same time hard as a rock and soft to the touch as the gentle hand of a mother.
YES! Immovable like a rock (faithful, true, honest...even brutally honest) yet a soft exterior like the hand of one's mother (patient, kind, for you, willing to sacrifice for your good).
Aren't these the kind of persons for whom you're most grateful in Your life? I can't help but think it's because they best model the "Velvet Steel" love of our Heavenly Father.