In the last letter of the word "Vayikra" (the first word of this week's Torah reading), the Hebrew alef is written in a smaller than regular size. We also find that some letters, such as the alef of the word "Adam" (in the first word of the first verse of Chronicles), the beit of the first word of the Torah ("Bereishit"), are written larger than regular size. In fact, in the twenty-four books of Scripture we find an entire alphabet of small letters and an entire alphabet of large letters; of course the vast majority of the letters are regular size. The Zohar of this week's portion discusses the significance of the small alef of "vayikra". It begins with a discussion between the Sages and a young schoolboy they meet while on a journey. They ask him to review his studies with them…

Completeness is to be found only in the Holy Land….

The young boy began his discourse with a verse: "He called to Moses. G‑d spoke to him from the Tent of Communion." (Lev. 1:1) Why is the alef of "vayikra" [Hebrew for "He called"] smaller [than regular letters]? Because Moses' being called was incomplete. For what reason? Because it was only in the Tabernacle [a temporary structure, unlike the permanent structure of the Holy Temple]. Also, because it was in another land [not in the Holy Land] for completeness is to be found only in the Holy Land.

Furthermore, here the Shechinah ­- the feminine aspect - called out to him. In other words, the revelation of G‑dliness was manifested only through the sefira of malchut. And that is why "vayikra" is written with a small alef - indicative of the aspect of malchut alone, when it is not unified with Zeir Anpin. Whereas there [in the Holy Temple] it is complete, comprising male and female aspects in a state of integration, therefore the alef of "Adam" in  "Adam, Shet, Enosh" (Chronicles 1:1) [is written in larger than regular letters, indicative of bina].

The revelation to Moses was only from the aspect of malchut….

Moreover, the end of the verse [also proves that the revelation to Moses was only from the aspect of malchut, since it states,] "and G‑d spoke to him from the Tent of Communion" alluding to the sefira of malchut. This is why the alef of "vayikra" is small.

Another explanation: the small alef [also alludes to Zeir Anpin when it descends into the Tabernacle]. This can be compared to a king: when he sits on his throne [in the palace - i.e. the Holy Temple] wearing his crown, he is called "the Exalted King". But when he descends [from his throne] to visit the home of his servant [i.e. the Tabernacle], he is referred to simply as "the King". So too, regarding the Holy Blessed One: when He transcends all things - the transcendent level manifested in the Holy Temple where malchut merges into the transcendent level of Zeir Anpin - He is called ["the Exalted King"]. But when He descends from His abode [to clothe His revelation within malchut] He is called "King" [only], not "Exalted King". And therefore the alef of "vayikra" is small.

[Zohar I, 239a, according to Or Yakar, Mikdash Melech, Matok MiDevash; translation and commentary by Moshe Miller]