Explain Aram's reaction when he saw the horse for the first time.

William Saroyan devotes quite a bit of space in his story entitled "The Summer of the Beautiful White Horse" to explaining Aram's reaction upon seeing the horse for the first time.
Aram, the narrator, is nine when his cousin Mourad comes to his window astride the horse. He is amazed by what he sees. It is four o'clock in the morning when his cousin awakens him, so he is in the dazed state of not quite full wakefulness. He has always dreamed of horses, as far back as he can remember. He has longed for a horse of his own from his earliest memories. But his family is poor. He describes this situation as an "amazing and comical poverty." He also knows his whole tribe has been famous for their honesty for eleven centuries. For these reasons, he tries to believe what he sees. His desire longs for what he sees to be true, but his logical mind won't permit him to believe it. He knows his cousin Mourad couldn't have afforded the horse. Then he reasons Mourad must have stolen the horse, but he can't reconcile himself to that conclusion either (due to the family's reputation for honesty).

I jumped out of bed and looked out the window. I couldn't believe what I saw. It wasn't morning yet, but it was summer and with daybreak not many minutes around the corner of the world it was light enough for me to know I wasn't dreaming. My cousin Mourad was sitting on a beautiful white horse. I stuck my head out of the window and rubbed my eyes. Yes, he said in Armenian. It's a horse. You're not dreaming. Make it quick if you want to ride.

Of course, Aram does jump out of the window and join his cousin. He then reasons that it isn't really stealing if they don't plan on selling the horse. In that way, they are only borrowing it without permission.