How can we be pebble-hearted?

What earnestness our theme deserves! We have to tell of an earnest Savior, an earnest heaven, and an earnest hell. How earnest we ought to be when we remember that in our work we have to deal with souls that are immortal, with sin that is eternal in its effects, with pardon that is infinite, and with terrors and joys that are to last for ever and ever! A man who is not in earnest when he has such a theme as this,—can he possess a heart at all? Could one be discovered even with a microscope? If he were dissected, probably all that could be found would be a pebble, a heart of stone, or some other substance equally incapable of emotion. I trust that, when God gave us hearts of flesh for ourselves, He gave us hearts that could feel for other people also.  - C.H. Spurgeon from "The Soul Winner"