The waving of the Arba Minim (the Four Species) — the Na’anu’im— serves as a focal point of the t’filot of Chag HaSukkot. Interestingly, though, one can fulfill his minimal obligation by merely picking of the Arba Minim (See Sukka 42a). However, the clear implication of many Rishonim is that Na’anu’im are a l’chat’chila d’Oraisa – a Biblically mandated ideal enhancement to the performance of the mitzva (see Rambam (Hilchot Lulav (7:9); also Tosfot and Ritva to 37b who rule stringently in case of doubt, presumably following the rule S’feika D’Oraisa L’Chumra). Indeed, the Mishna in Masechet Sukka (29b see Rashi there) indicates that unlike the Hoshana (myrtle) and Arava (willow) whose minimum size is three t’fachim (handbreadths), the Lulavrequires 4 t’fachim. The extra tefach, as the Mishna explains, is necessary “k’dei l’na’nai’a bo” — in order to wave it. Although the Ba’al Ha’Itur and Me’iri maintain that this requirement for the fourth tefach is only Mi’d’rabbanan, the overwhelming majority of Rishonim and subsequent Poskim maintain that 4 t’fachim is an absolute requirement which would seem to indicate its Biblical origin. Even though the Na’anu’im are only l’chat’chila, the lulav must at least be fit for waving.
What is signified by this Biblically mandated waving? Furthermore, it is clear from the Mishna (37b) that the Four Minim are to be waved at two places in the Hallel — once at “Hodu Lashem Ki Tov” — “Give praise to G-d for He is good” and once at “Ana Hashem Hoshi’a Na” — “Please G-d, save us now!”. These expressions contain drastically different themes. “Hodu” is a call to praise Hashem for his everlasting kindness. “Ana” is a heartfelt prayer for salvation. How does the waving of the Arba Minim enhance these diverse prayers?
What clearly emerges is that the waving of the Arba Minim serves as both a t’fila of bakasha (request) and a song of hoda’ah (praise). But how does the lulav accomplish both tasks? The Mishna in Rosh Hashana (16a) relates that “Be’chag nidonin al ha’mayim” — on Sukkot the world is judged concerning the amount of rainfall for that year. The four species all require additional watering in addition to rainfall to survive. The Torah even refers to Aravot as Arvei Nachal — willows that grow by a river. There is even a minority position in Tosfot (34a) that the Aravot must grow by a river to be valid. Even though we do not follow this position (see Shulchan Aruch (647:1) and Mishna B’rura (3)), certainly the Torah highlights the role of water in the Arba Minim. Indeed, one of the textual proofs that the Biblical “Pri eitz hadar” (Leviticus 23:40) is a citron is that the word “hadar” is etymologically related to the Greek “hydro” meaning water (Sukka 35a). Hence, the Torah refers to a fruit that needs much additional watering to survive. The waving of the species then, is a form of t’fila for rain. Besides the t’fila for rain on Shmini Atzeret, we pray every day of Sukkot for rain in the Hallel by waving the Arba Minim at “Ana“.