Destiny?

At the end of chapter nine, we come across a passage which we had already seen in chapter three:

God Grant me
The serenity to accept
The things I cannot change
Courage
To change the things I can
And wisdom always
To tell the difference.

It was first mentioned when Billy travels back in time to his optometry office. The passage was framed on his wall to give his patients hope. In chapter nine though, it was engraved in Montana Wildhack`s locket. I don’t believe that it was simply coincidence that these two characters happened to end up as captives in Tralfamadore. This passage had to have meant something for Billy, Montana, and most importantly, the Tralfamadorians. Although I am not sure yet, I think it has something to do with the following phrase from chapter three: “Among the things that Billy Pilgrim could not change were the past, the present, and the future.” It all relates to time and free will. Maybe this explains the serene attitude that Billy adopts throughout the entire novel, even when he is capture and brought to another planet. He always keeps calm and accepts things the way they are, because he knows that time is something that cannot be changed. But how would this relate to Montana? On earth, she was no more than a superficial teenage movie star, who would occasionally make adult films. She`s not different from other humans in the way Billy is, therefore makes no sense why she was chosen over anybody else.

There is another way to think about this situation though, and it is by eliminating the theory that there was a reason behind it all. On the night that Billy was kidnapped, he asked the Tralfamadorians why they had picked him. Their answer was: “Because the moment simply is…Well here we are, Mr. Pilgrim, trapped in the amber of this moment. There is no why.” Maybe there is no explanation behind this, other than the fact that the moment was simply meant to happen.

I personally doubt the Tralfamadorian reasoning, for I am sure that there is more mystery to life and to this book than what may be told. Unfortunately, I was unable to find an explanation, in order to make all the pieces of the puzzle.