Why is the Qur'an necessary in Arabic?

http://www.ce.berkeley.edu/~coby/essays/refdigl.htm

It’s a warm Friday mid-afternoon in a village in the Peruvian Highlands, not far from Cuzco. In the main plaza, a small crowd consisting mostly of women and young children – some of elementary-school age, some pre-school – is chatting in Quechua, seemingly waiting for something to arrive. And , sure enough, something does arrive: a brightly painted school bus, which stops near the crowd and disgorges a dozen or so neatly uniformed high-school students. It’s their families who have been waiting for them. But before these older boys and girls join in the Quechua chatter with their mothers and younger siblings, they bid farewell to one another and to their schoolmates who stay on the bus to go on to the next village. They talk about plans for the weekend – soccer, movies – and for the following week. How do I know this? Because this conversation is in Spanish, not Quechua.