Of course he have the ability to speak, but if he don't...
Craft is the more prominent feature of literary art than inspiration.
"Practice makes it perfect." Many people write inspired drivel. It takes hard work and practice to be great. "Inspiration is a necessity, while craft is a tool." I think you have to consider that statement again. the simplest example I can say is language. When a kid is born, he is not "born with" the language but, he is "learning" the language. Of course he have the ability to speak, but if he don't use it he will lose that ability forever. So, he have the "inspiration" but not the "tool" and hence, he won't have any use with his "inspiration." As you said "inspiration is just the motivation behind writing". That motivation won't always make a good writer. It needs work too. "How does reading another work motivate one to write?" I considered that question as well. But think about it. Suppose, you are an inspirational writer and you wrote so many works. But now, after you have written down all of your ideas on a piece of paper, you wouldn't know what to write next. So you try reading the famous works of other writers. I don't mean plagiarism, but, when you read a book based on a certain theme, you are evoking your ideas relating to that theme.