'Fly a Little Higher': Mother reflects on son's death, and his songs that live on

In May 2013, 18-year-old Zach Sobiech died of osteosarcoma: bone cancer. When it became clear that Zach had months to live, his mother Laura suggested he write letters to family and friends. Instead Zach picked up his guitar and started writing songs. One of them, the hauntingly beautiful "Clouds," began to spread online. The song's official video has been viewed more than 10 million times, and the celebrity tribute featuring Bryan Cranston, Jason Mraz, Ed Helms and Sarah Silverman has more than four million views.

Now Laura Sobiech has written the moving book 'Fly a Little Higher' about her son's illness and death. She spoke to FOX411 about her extraordinary son and how faith helped her deal with his illness and passing.

FOX411: What message do you want to get across with this book?

Laura Sobiech: What I wanted to get across is we're ok, Zach was ok. This idea that your life is destroyed if somebody close to you dies or if your life is cut short. We get so freaked out about it in our culture. All this energy is put into prolonging life. Life is precious and we should fight for it but at some point you have to decide how much energy you're going to put into more physical life or do you start focusing on spiritual life. For us it was preparing Zach to die. Especially when you're dealing with parents. I think that's an important message. I saw people who weren't preparing, they were kind of in denial, they weren't preparing their kids to die and when their child dies they're completely devastated. I think it's ok to say, 'We're going to prepare for this.'

FOX411: That took so much courage to talk to Zach about how he wanted to die.

Sobiech: It was one of those things I knew I had to write about. It needs to be ok. The way we treat death, the way we get freaked out, it's almost like we're ashamed of it. Like we have this denial because we can't deal with it. It's here, it happens and you have to deal with it. It was tough but I think it really helped him because it made it ok for him to die.

FOX411: How did religion help you cope?

Sobiech: We're Roman Catholics. We've been practicing Catholics our whole lives. One of the things about being Catholic is we have an understanding of suffering that I think is kind of unique, that it's worth something. That suffering can be a channel of God's grace into the world even if you don't see it, even if it's not directly connected to you. It still can benefit the world and I think that was one of the the big things, personally for myself and Zach kind of understood. When you suffer it doesn't have to ruin your life. If you put it in the context of something bigger then it can make some sense, even if it doesn't make sense, you know it's worth something, that being a base of understanding, what was going on and that we weren't being punished. Also to know that this isn't it. We believe in eternity with God. This is sort of the ante-chamber so to speak and knowing that there is something beyond this - that all helps. We really feel like he's not physically present but I feel very, very close to him.

FOX411: Do you ever ask, 'Why Zach?'

Sobiech: I don't know why it had to be. But what I do know and what we've been so blessed as a family to have witnessed is on so many levels look at the response of people to his music and his life. As something as simple as the osteosarcoma research team that we're helping right now is in our backyard and that happened the year before Zach got cancer. I'm able to see, ok maybe that's why it was him. Here's this kid who is bringing all this attention to this disease now. There's all sorts of pieces I can put together and try to make sense out of but I can't see that big picture like God can. Maybe someday I'll understand it. I just have to be ok with it.

FOX411: Were you ever angry?

Sobiech: No, and I knew as we were going through this whole thing that that was just a gift that I didn't have to struggle with anger. My husband Rob did. He went through that period of really wrestling with God. He's a rules guy. It didn't make any sense to him why God would do that to us. But he did come to some measure of peace and trust too.

FOX411: You're very honest in saying that Zach's illness put a terrible strain on your marriage, which is very common.

Sobiech: That was something that Rob had to trust me to write about. It was not easy for him to allow me to write. It was important for me to be able to be honest about that stuff. I don't think we're doing anyone any good when we hide that stuff and don't talk about it. I don't want people to look at our family and go, 'Oh they're perfect, of course they got through this,' because that's not the case. I think that makes the story even more hopeful because, yeah, we did struggle.

FOX411: Are you amazed at the response to Zach's music?

Sobiech: Oh yeah, I still can't really wrap my head around it. It's one thing to have people listening to it, it's quite another to get messages from people all over the world saying, 'This song changed my life.' They're actually writing us letter or tracking down our phone number. They have this real need to tell us, 'This has changed me.' That's where I can step back and say, 'Oh this is so much bigger than any of us.'