Baruch Hashem, we have the privilege now of starting Sefer Vayikra -- and where better to start than the first word of it?
#1: Says the Yismach Yisroel (the second Aleksander Rebbe -- Rebbe Yerachmiel Yisroel Yitzchok Danziger zt”l), the small א in the word ויקרא teaches us that every single thing in life -- no matter how “small” it might seem -- is Hashem calling us (as Vayikra means ‘And He called’). (From Torah Wellsprings; an online Chassidus booklet compiled by Rebbe Boruch Twersky shlita and sent out by my Rebbe, HaRav Tal Moshe Zwecker shlita).
#2: It appears to me that the small א carries a huge message in life: Some people, may Hashem save us, (especially children, likely) mistakenly think that the people who look so great and boast of their riches, greatness, etc. are the great and successful people -- so that is how they can show others they are great as well!
But this is not the truth: With the small א here, the holy Torah teaches us that, you know what a great person is (symbolized by the א -- the first letter in the Aleph-Beis)? Someone who is humble and not always trying to show off. That is a true א person!
And, inspired by a title of part of a Vort by HaRav Shimshon Dovid Pincus zt”l (in Tiferes Shimshon), perhaps we may say that this is why children (at least used to) start with learning Parshas Vayikra: Because one of the first things a child should learn is to to be humble, and not arrogant, Chas V’Shalom.
#3: The letter אל”ף (if spelled out), notes the Kli Yakar zt”l, has the connotation of teaching, for it has the same spelling as the word that is sometimes used to mean ‘teach’ -- אלף.
#4: “Says Rabbi Assi: Because of what do children begin [studying Torah] with Toras Kohanim (Sefer Vayikra)? But because children are pure and Korbanos are pure. Let pure ones come and engage in pure things.” (From Midrash Vayikra Rabbah).
Inspired by the title of part of the Vort from Rav Pincus zt”l on this Midrash, perhaps we may say that one of the most extremely important foundations for a child to learn is pureness. This is one of the foundations of life -- and very important to learn at a young age.
But overall, one of the big lessons we learn from the small א is how much can be derived from every last detail in the Torah: From one letter -- small letter even -- there are so, so many insights and lessons to be gleaned. Just imagine one word, or sentence! Indeed, the holy Torah is endlessly deep.