Vayikra: Hearing, and answering, our calling

I recently received this story via email: 

A lady passing a young boy on the street noticed he was entranced by a pair of shoes in a store window. “My, but you’re in such deep thought staring in that window!’ she said.

“I was asking G-d to give me a pair of shoes,” was the boy’s reply.

The lady took him by the hand, went into the store, and asked the clerk to get half a dozen pairs of socks for the boy. She then asked if he could give her a basin of water and a towel. When he brought them to her, she took the little fellow to the back part of the store and, removing her gloves, knelt down, washed his little feet and dried them with the towel. 

By this time, the clerk had returned with the socks. Placing a pair upon the boy’s feet, she purchased him a pair of shoes.

She tied up the remaining pairs of socks and gave them to him. Patting him on the head she said: “No doubt, you will be more comfortable now.”

As she turned to go, the astonished kid caught her by the hand and, looking up with tears in his eyes, asked her: “Are you G-d’s wife?”

This week we begin the book of Vayikra (Leviticus), whose name, which means “And He [G-d] called,” is taken from the first word of the first verse in the book: “And He called to Moshe, and G-d spoke to him from the Tent of Meeting” (1:1).

Rashi points out that this is an unusual turn of phrase; normally G-d speaks to Moshe, whereas here G-d calls him. Indeed Rashi notes that when Balaam (the Gentile Prophet viewed by Jewish tradition as being a wicked personality) speaks with G-d, the word used is “vayaker,” meaning “G-d happened upon him.” The difference in these two Hebrew words is simply the letter Aleph. In a traditional Torah scroll, the Aleph appears as a smaller letter, suggesting a difference between experiencing something as a coincidence and as a calling.

Rashi also notes (1:1) that when Hashem called Moshe, only Moshe could hear Hashem’s voice and other people were unaware of G-d’s calling. Why does this unique calling of Moshe (as opposed to the more frequent description of G-d speaking to Moshe) occur here at the beginning of Vayikra?