Vayikra means "And He called." It is the name of the third Chumash and the first word of that Chumash.
When we look at the word Vayikra, we can see that it has an unusual sized letter. The last letter of this word, the alef, is very small.
This is not the only alef in the Tanach which is of a different size. In the book of Divrei HaYomim, there is another irregular alef. It is in the word Adam, in the possuk which tells us the order of the generations beginning with Adam HaRishon, the very first man.
The alef in the word Adam is not small like the alef in the word Vayikra. Quite the opposite. This alef is oversized, larger than the other letters.
We can learn something about Adam HaRishon from the oversized alef in his name. Adam knew he was very special, because he was created by HaShem's own hands. He felt very sure about himself, so sure of himself that he wasn't careful and he made the mistake of eating from the eitz hada'as.
Every person should know how special he is, but he should not become proud or careless. Moshe Rabbeinu surely knew that he was special. After all, he was the only one to speak to HaShem "face to face." Yet, Moshe felt more humble than any other person. He used to tell himself: "All that I have is a gift from HaShem. If HaShem had given these opportunities to someone else, he surely would have been much better than me."
Moshe Rabbeinu considered himself smaller and less important than others. That's why there is a little alef in the word Vayikra. Rashi tells us that HaShem's calling Moshe was a sign of special care. HaShem loves humble people. Because Moshe was so humble, HaShem called to him and showed him special attention.
We are all children of Adam and each of us has a spark of Moshe Rabbeinu in his neshamah. To be as great as Adam could have been, we have to act small and humble, as Moshe did.
(Adapted from Likkutei Sichos, Vol. XVII, Parshas Vayikra)