We say (in Modim), יום שבכל נסיך ועל ...לך נודה עת שבכל וטובותיך נפלאותיך ועל עמנו, "We praise you...for the miracles You do for us each day and for Your wonders and kindness, which are constant."
An ideal time to recognize all the miracles that Hashem does for us is during the month of Adar. The Meor Einayim teaches that אדר stands for 'א,דר, the Alef, (Hashem, the עולם של אלופו) dwells. During Adar, we discover that Hashem dwells in this world, helping us and performing miracles for us all the time.
Chazal (Beitzah 15:2) say, נכסיו שיתקיימו הרוצה אדר בהן יטע, "If one wants to ensure that his property will remain with him, he should plant an adar." The Bnei Yissaschar (Adar 1:8) explains that he should implant into his heart the lessons of Adar, the emunah that Hashem dwells in this world, and everything is from Him. This emunah will grant him success and wealth.
The Ahavas Shalom zt'l says that אדר is roshei teivos for אשתכח דרעוין רעוא, "The desire of all desires prevails." This means it is a month of eis ratzon, when Hashem's love and desire for us are expressed and felt profoundly.
The Yeshuos Yaakov zy'a (the Lemberger Rav) met with Rebbe Eizik of Zidichoiv zy'a and said, "I heard that you don't say tachanun throughout the month of Adar. Tell me a source for this custom of not saying tachanun. And, please, don't give me a source from kabbalah or chassidus. I want a halachic source."
Rebbe Eizik Zidichoiver replied, "It states (Esther 9:22) ומאבל ,לשמחה מיגון להם נהפך אשר והחודש טוב ליום, 'The month that was reversed for them from grief to joy and from mourning to a Yom Tov.' So, the entire month became like a yom tov, and we don’t say tachanun on a holiday."
