I believe this is a very big part of the freedom that God gives us in him- as we grow to know him more personally, he brands his ways on our hearts. No longer must I refer to a mental or physical list of "how to be a Christian". His Spirit stirs change in the obscure corners of my heart, to the point that I hardly notice until I find myself acting or reacting in a very unKatie-like way.
I believe he comes, grows, and abides in us in much the same way as he came, grew, and left a Comforter here on this earth.... quietly, personally, gently yet powerfully and most of all- undeniably.
Changed heart, changed world.