A missing piece of your heart 

"This human heart of yours is not perfect in shape as a valentine heart.  There's a small piece missing out of the side of your heart and out of every human heart. That is the piece that was torn out of the universal heart of humanity on the cross.  When God made your heart and every other heart, he found it so good that he kept a small sample of it in heaven and then sent the rest of it into this world where it would try to fill up all the love it could, but where it would never be really happy, never totally in love, never able to love anyone with a whole heart because it hasn't a whole heart to love with.  It will never be happy until it goes back again to God to recover that piece that he has been keeping for it from all eternity."