Vayikra means "And he called." It is the name of the third Book of the Torah, and its first word.
When we look at the word Vaikrá, we can see that its last letter, the Alef, is smaller than usual.
Elsewhere in the Tanakh, we find the opposite. In Divrei HaYamim, the name of Adam HaRishon (the first man) has a larger Aleph than normal.
We can learn something from these two irregular letters. Adam HaRishon knew he was a special person; he was created with the very hands of God. He felt so confident that he was careless and ate the fruit of the Tree of Knowledge.
On the other hand, Moshe also knew how special he was. God spoke to him "face to face." Yet, he was the "humblest of all the earth." He used to say to himself, "Everything I have is a gift from God. If God had given these opportunities to someone else, they would surely have been better than me.""
The small Aleph in Vayikra refers to Moshe. The large Aleph in Divrei HaYamim refers to Adam HaRishon.
We are all children of Adam, and we all have a spark of Moses within us. Even if we are as great as Adam was, we must conduct ourselves with the humility of Moses so as not to fall into error.
Adapted from Please tell me what the Rebbe said