He called to Moshe, and Hashem spoke to him from the Ohel Moed.
Look carefully at the pasuk. The line opens with an unidentified “He.” Of course, it does not take too long before we learn in the next phrase that it was Hashem who called to Moshe. Why does the identification have to wait at all? Why does the Torah not write, “Hashem called to Moshe, and spoke to him?” We learn here of a process that applied to our nation in its infancy, and to a great many individuals to this day.
A person kept in complete darkness for a long period of time cannot tolerate light. To make him visually functional, you need to first expose him to the smallest sliver of light, perhaps through a hairline crack. As his eyes adapt, you can gradually widen the crack, and let increasingly more light in. In time, he can move to a place with conventional lighting.
Similarly, Hashem brought them to the point of our pasuk in a journey of small steps. He first took the Bnei Yisrael out of Egypt, gave them just the few mitzvos of milah and pesach, split the Reed Sea, displayed His presence continuously with clouds of glory by day and a fiery pillar at night, and brought them to Sinai to receive the Torah. Only then did He command them to construct a mishkan that would cause His presence to reside within them.
Hashem similarly deals with the individual. He contracts Himself – allowing only a bit of his light to shine through – to be available to each and every person. Included in this are even evildoers. Evidence of this can be found in the occasional thoughts of teshuvah that cross the mind even of the rasha. These are nothing less than Hashem calling to him – beseeching him to return – even though he remains unaware that Hashem has planted these thoughts in his consciousness.
Here we have the meaning of the unusual way of writing the word Vayikra/He called. In our Torah scrolls, the last letter of that word is an undersized aleph. It stands for Alufo Shel Olam/the Chief of the world. It indicates that He is available to every Jew, albeit in a contracted presence, in calling him to teshuvah. Initially a person does not understand the source of the call. At times, he has regrets and recriminations, and wonders if he should mend his ways.
He may, in time, come to realize that G-d has been the One prodding him. At that point, Hashem can speak more openly to him from the Ohel Moed. As he makes slow progress, he will find that he will sometimes attempt to sin, but find himself unable. His hand will be stilled, as it were, from Above. He will realize that Hashem is speaking directly to him, plaintively saying, “Return to Me! How long will you pursue emptiness?”