Just as with the beginning of Av rejoicing is curtailed so with the beginning of Adar rejoicings are increased (Taanis 29a)
These days shall be transformed to days of joy and happiness, which is through Simcha shel mitzvah, as it’s brought in seforim regarding what the gemara says about curtailing joy in Av (and connecting it with and) similar to Adar, that when Adar begins we increase in joy. This means, that when Adar comes, how can a person increase in the theme of Adar (i.e., joy) is by increasing in Simcha itself.
In similar fashion – they explain – is also regarding Av, when “with the beginning of Av memaatin [how do we diminish the issues of Av this is through being more] joyous”
It should be a double consolation, which is not only double, but incomparably dis-proportionate, as we find regarding the second Luchos (Nedarim 22b) which added the twenty-four seforim (Neviim and Ksuvim) and Mishna, Halachos, Agada etc.
As the Alter Rebbe writes in Igeres haTeshuva (ch. 9) a baal teshuva who was accustomed to learn...should learn etc.. Similarly, through simcha shel mitzvah, and especially in these days, we come to a double consolation, a double salvation in the true and complete Geula through Moshiach tzidkeinu very soon in our time.
(Sh”P Devarim 5730)
