The Book

May I tell you another one? If I'm turning into a pest just say so... LOL
Like all those before, this story is true, with no exaggerations. My mother's good friend lost her son. He was nice young man, hard working, never in trouble. Even the accident in which he was killed wasn't his fault. We were all shocked and sad but, of course, not near as much as his mother. She is a devout Catholic but still couldn't find any comfort.
For weeks she sat in her room and cried, went out only to go to cemetery and church. Family and friends started to worry, nobody expected her to cheer up but it was time to continue her life.
Then suddenly, over night, she went back to her usuall care about family and home, even to her hobbies. Nobody dared to ask anything, but she told my mother what happened: She was going to the evening mass and approaching the church she saw a young man standing at the church's door. With each step closer it was more and more clear it was her son. He had calm and almost happy expression on his face. But when she got close, few steps between them, he smiled, gently shook his head, and disappeared. She stood there for a while, shocked, until some of her friends got to the church as well, asking her: «What's the matter, are you not coming in?»
It was too soon to mention anything, she was still processing the whole thing.
Later at home, she was sitting in her armchair trying to rationalize, staring blank towards the book shelf. And one book got out of the row, over the edge and fell to the floor. She got up calmly, picked up the book, one of her son's favourites. From that point on, life became bearable again.
I know what sceptics will say, her mind tortured with utter sadness generated her son's image. OK, who made the book fell then?