I
"Just as we decrease joy in the month of Av, so should we increase joy in the month of Adar" (Ta'anis 29a). The expression "just as" (k'shem) implies a logical connection between the two halves of the statement. What is this connection?
The destruction of Tisha B'Av was caused by the sin of the spies which took place on the same date in the desert (ibid.). This sin, often understood as an act of cowardice, is explained by the Zohar in a totally different light. The spies, being great leaders, were afraid of spiritual decline in Eretz Yisrael. In the desert, the Jews' needs were provided by Hashem's miracles, and they were free to spend day and night studying Torah. Upon crossing the Jordan, they would be required to begin a new lifestyle in which much of their time would be devoted to agriculture and other mundane matters. The spies feared that this change would adversely affect the Jews' spirituality, and they attempted to prevent it by their report of danger.
If this analysis is correct, why was the spies' action such a grave sin? The answer is that Hashem wants the Jews to maintain their sanctity despite the challenges of everyday life. The supernatural era of the desert, critical to the development of the Torah nation, was not its ultimate mission. The attempt of the spies to frustrate the fulfillment of the Divine plan, even if sincerely motivated, was an error of tragic and eternal consequence.
The punishment for this sin was the challenge to maintain spirituality and faith despite conditions even more difficult than those in Eretz Yisrael. The only way for the Jews to atone for their sin of trying to avoid the spiritual difficulties of Eretz Yisrael was to overcome even greater difficulties in the galus. Thus the destruction of Tisha B'Av resulted from the sin of the spies.
The Jews passed this critical test of their faith in galus during the events in Shushan which we commemorate on Purim. They maintained their spirituality despite the threat of total annihilation. This was the atonement for the sin of the spies, and as such, calls for an increase in joy, just as the remembrance of the sin itself and the resulting destruction decreases our joy in Av.
II
Amalek came and battled Yisrael in Refidim (Shemos 17:8). Amalek attacked because the hands of Yisrael weakened (Refidim=rafu yedeihem) with respect to Torah (Mechilta).
Hands represent worldly pursuits, commonly performed with one's hands, as opposed to purely spiritual matter performed with one's mind and/or mouth. Amalek attacks when we falter in our mission of consecrating otherwise mundane aspects of life, such as earning a livelihood, eating, and the like. When our hands weakened in Refidim, we became vulnerable to our archenemy Amalek's attack.
Moshe's hands grew heavy, and Aharon and Chur supported his hands (17:12). Moshe represents purely spiritual life, which enable him to go without food or drink for 40 days and nights when he ascended to receive the Torah (Devarim 9:9), and which required him to abstain from relations with his wife (Rashi Bamidbar 12:8). As a result, his hands were heavy. He could not lift his hands, symbolizing the elevation of worldly pursuits, because he was exceedingly spiritual.
Similarly, Moshe's mouth and speech were heavy (Shmos 4:10). Speech combines the physical body with the spiritual soul (Onkelos Bereishis 2:7). Moshe's heavy speech reflects not only an impediment but also a uniquely spiritual personality (Maharal, Gevuros Hashem Chapter 28).
Moshe delegated Yehoshua to fight Amalek (17:9). Yehoshua combined the spiritual and physical and could battle Amalek who attempts to sever the connection. Later, he would be saved from the plot of the spies, who also wished to live a totally spiritual life.
The name Kah combines the spiritual yud with the physical heh. It is this name of Hashem that saves Yehoshua (Kah Yoshiacha) from the spies (Rashi Bamidbar 13:16). And it is this name which is used to express Hashem's eternal battle against Amalek (Rashi Shmos 17:16).
Aharon was chosen to support Moshe's hands. As a kohein, Aharon's role is to sublimate physical objects, such as animals, flour and wine, by offering them and even by eating them to achieve atonement (Pesachim 59b). Moshe's pure spirituality disqualified him from serving as a kohein, a role which Aharon assumed (see Rashi Shemos 4:14). For the same reason, Moshe could not lead us in Eretz Yisrael, the place which required combining physical and spiritual, a role which Yehoshua assumed (Vayikra Raba 11:6).
III
Amalek heard that Aharon had died, and fought against Bnai Yisrael when we came to the way in which the spies went (Rashi Bamidbar 21:1). This second attack of our archenemy was launched at a time that the connection between the physical and the spiritual was weakened by the death of its primary practitioner, Aharon Hakohein. It took place at the location in which the connection had been severed earlier by the spies (Asufas Maarachos by Rabbi C. Y. Goldvicht z"l).
The commandment to destroy Amalek (Devarim 25:19) is followed immediately by the mitzvah of bikkurim (26:1-4). This mitzvah is referred to as "trumas yedchem," the lifting up of your hand (Rashi 12:6). When we destroy Amalek, we are able to lift our hands, to take the first fruit to the kohein, thereby elevating all of our harvest to a spiritual level.
Every meal is preceded by netilas yadayim, lifting of the hands. We thereby fulfill "lift your hands to sanctity" (Tehillim 134:2). Eating is the ultimate physical activity. Instead of eating like animals, we are to begin our meal by lifting our hands, and consecrate it by reciting proper berachos before and after.
In parshas Terumah, we read about the mizbeach (Shemos 27:1-6). Nowadays, one's table achieves the atonement that the mizbeach achieved when the Beis Hamikdash stood (Menachos 97a). This is accomplished by inviting the poor, and by reciting words of Torah (Maharsha, based on Berachos 55a and Avos 3:4). Additionally, the exercise of self-control in leaving over some of the food is a self-sacrifice which achieves atonement (Maharsha Bava Basra 60b) - as well as character refinement (Rambam T'shuva 7:3) and good health.
In the month of Av, when we proved unable to elevate the physical, we limit the joy of eating, culminating in the fast of Tisha B'Av. In the month of Adar, when we defeated Amalek, thereby sublimating the physical, we increase the joy of eating, culminating in the Purim se'uda. This joyous se'uda should include, or be accompanied by, helping the poor (see Rambam Megillah 2:17). It must contain words of Torah. And it must be governed, even on Purim, by appropriate self-restraint. In this way, we can all participate in destroying Amalek by consecrating all aspects of our lives.