One of the major themes in Alice Sebold's The Lovely Bones has to do with the power of love to guide the process of grieving and healing.  When the novel opens, the reader learns immediately that Susie Salmon is already dead.  As the novel unfolds, Susie's family is shown at various points in their grief over Susie's death and then grappling with the knowledge that she has been murdered.  Susie's father Jack takes Susie's death particularly hard and goes through every possible method to try to find her body and her killer.  He continues this struggle even after the authorities have given up much hope.  Some might argue that Jack becomes obsessed with his search for the truth and that he is not allowing himself to accept Susie's death.  However, as time moves on, his love for Susie takes over him and he begins to process his grief so that he can move on with his life.

Similarly, Susie is caught in the "in-between."  She cannot move on because there are many things that she has left undone, namely her unrealized love for Ray.  She regrets that she never got to have a first kiss, so she takes over the body of Ruth so that she can come back to kiss Ray.  After this expression of love, Susie can move on into the afterlife.

So, The Lovely Bones has to do with the power of love to aid in grief and healing.