I have struggled with this and will struggle with this forever. I will never know why Lauren specifically has Autism. Why is it that out of 150 kids she couldn't have just been one of the 149? I will never know on this side of eternity. I may know of the other side but my hope is that I will be so busy worshipping, dancing, and signing that I won't care.
I can answer the question of why Lauren has Autism in a general sense. We live in a fallen world. Disease and disorder is all a part of the fallen world we live in. Autism is no exception.
The other reason is so that God may be glorified in all of this. It is He, and He alone, that gets the glory. A special needs child has made me cling to His promises like never before.
Bob and I find great comfort in this story from the New Testament (a paraphrase)
The Pharisees were questioning Jesus and asked about a blind man. They asked who sinned the man or his parents. Jesus replied "Neither, for this is done so that God may be glorified in this"