We now turn to Sukkah, chapter 3, mishnah 15, which deals with handling the lulav on Shabbos and Yom Tov, and with a child's obligation in the mitzvah of lulav.
"Mekabeles ishah miyad benah umiyad ba'alah, umachziraso lamayim b'Shabbos" - a woman may take the lulav from her son or from her husband and return it to the water on Shabbos.
It was customary to stand the lulav in water in order to keep it fresh, and the mishnah teaches that it may be returned to the water even on Shabbos. This relates to the reality that existed while the Beis HaMikdash stood, for as we mentioned earlier, when the first day of Sukkos fell on Shabbos the lulav and esrog were taken, both in the Beis HaMikdash and outside it.
There is no concern here of watering plants, since the lulav is already detached, and the woman is not assisting its growth but merely preserving it in its present condition. This halachah was stated even regarding a woman, who is not obligated in the mitzvah of lulav; nevertheless she is permitted to take the lulav, and according to the Ashkenazic practice even to recite a berachah on it, and therefore she may do so on Shabbos as well. Of course, nowadays the lulav is not taken on Shabbos, even when the first day falls on it.
The words of Rav Yehudah - the distinction between Shabbos and Yom Tov:
On Shabbos: as the first tanna stated, one may only return the lulav to the water.
On Yom Tov: one may even add water, and even change the water, since this does not involve excessive exertion that would be forbidden on Yom Tov.
"Katan hayodea l'na'anea chayav b'lulav" - a child who knows how to shake the lulav is obligated in lulav.
A child who knows how to take the lulav and esrog and to shake them properly - there is a mitzvah to train him in the mitzvah of lulav, since he is capable of fulfilling it correctly.
In summary: in this mishnah we learned that one may return the lulav to the water on Shabbos, because this is merely preserving its condition and not assisting its growth; that on Yom Tov both adding water and changing it are permitted; and that a child who knows how to shake the lulav is obligated in lulav by virtue of chinuch.