Question:
How important is it to hold the lulav in the correct hand? Which hand should hold the lulav and which should hold the esrog? Does the law differ for a left-handed person, and what should one do if the species were accidentally held in the wrong hands?
Answer:
The requirement to hold the lulav and esrog in specific hands is a well-established halacha and should be followed throughout the performance of the mitzvah. A right-handed person holds the lulav together with the hadassim and aravos in the right hand and the esrog in the left hand. A left-handed person does the reverse, holding the lulav with the hadassim and aravos in the left hand and the esrog in the right hand.
The reason for placing the lulav in the dominant hand is that the lulav bundle represents three of the four species, namely the lulav, hadassim, and aravos, while the esrog represents only one species. Since the more significant portion of the mitzvah is held in the dominant and therefore more honored hand, the lulav bundle is given precedence.
This requirement applies not only during the initial fulfillment of the mitzvah, but whenever one takes the Four Species for the sake of the mitzvah, including during Hallel and Hoshanos. Chabad custom, following the ruling of Admur and the practice of the Rebbe, is to be careful to maintain the proper hand placement throughout all the shakings of the lulav.
Nevertheless, if a person accidentally reversed the hands and held the lulav in one hand and the esrog in the other, he has fulfilled his obligation according to the accepted halacha. However, since some opinions maintain that one does not fulfill the mitzvah when the species are held in the wrong hands, it is proper to repeat the taking of the lulav in the correct manner without reciting another blessing.
Regarding a left-handed person, there is a well-known dispute among the authorities. The ruling of Admur and the Rama is that a left-handed individual follows his personal dominant hand and therefore holds the lulav in his left hand and the esrog in his right. Other authorities, including the Mechaber, maintain that a left-handed person should hold the species like everyone else, with the lulav in the right hand and the esrog in the left. Due to this debate, some Sephardic authorities recommend that a left-handed person take the Four Species both ways. Nevertheless, the accepted Chabad custom follows Admur and the Rama, placing the lulav in the left hand and the esrog in the right.
In summary, holding the species in the proper hands is an important detail of the mitzvah and should be observed carefully. However, unlike certain requirements that invalidate the mitzvah entirely, holding the species in the opposite hands does not generally prevent one from fulfilling the obligation after the fact.
Sources:
Admur 651:13-14; Siddur Admur; Hashlamas Divrei Nechemia 651:14; Rama 651:3; Michaber 651:2-3; Sukkah 37b in name of Rava; Magen Avraham 651:6, 9; Taz 651:2, 4; Ben Ish Chaiy Hazinu 14; Chaim Ubracha 186 in name of Yerushalmi; Mishnah Berurah 651:15, 19; Kaf Hachaim 651:32, 38-39; Otzar Minhagei Chabad p. 315; Moadim Uzmanim 2:121; Piskeiy Teshuvos 651:6