Chazal say בשמחה מרבין אדר משנכנס, "When Adar arrives, we should be very happy". The holy Ruzhiner zt'l teaches that one way to be in a state of happiness is to believe that Hashem will help us right away. Whatever a person is going through, he believes that salvation is just around the corner, and soon everything will become better. Hashem says (Tehillim 91:15) בְצָרָה א ָנֹכִי עִמּוֹ, "I am with him in distress." Hashem suffers our pain together with us. Hashem is the רחמים בעל, and He will certainly have compassion on us.
It states (25:3, 5) זָהָב מֵאִת ָּם תִּק ְ חוּ ֶׁראֲש הַת ְּרוּמָה וְזֹאת שִׁט ִּים וַעֲצֵי ...ֶׁתוּנְחֹש וָכֶסֶף, "This is the donation that you shall take from them: gold, silver, and copper... and the woods of Shitim." Rashi asks: From where did they have עֲצֵי שִׁט ִּים in the desert? Reb Tanchuma explains that Yaakov Avinu saw with his ruach hakodesh that the Yidden would build a Mishkan in the desert, so he brought ארזים, cedar wood to Mitzrayim, and he planted them there. He told his children that when they leave Mitzrayim, they should take the wood along with them.
Why was Yaakov Avinu concerned specifically about the שִׁט ִּים עֲצֵי in the desert? The other items that were needed for the Mishkan weren’t available in the desert either. For example, they needed precious gems for the eifod, and they needed the skins of a תחש to build the Mishkan. Hashem supplied them with their needs in the desert when they needed them. The Gemara (Yoma 75a) says that the gems fell with the manna, and Hashem created the תחש animal for that short period of time, and they were able to build the Mishkan. Just as Hashem provided the gems and the skins of the תחשים, Hashem could have provided the שיטים עצי, as well. Why did Yaakov see it necessary to plant them so that they would have them in the desert?
Tzaddikim (Vayechi Yosef, Terumah, and the Lubavitcher Rebbe zt'l) answer that Yaakv Avinu planted the שיטים עצי in Mitzrayim to give hope to the Jewish nation. While in Mitzrayim, they noticed the שיטים עצי, and it reminded them that one day, Hashem will free them, and they will build a Mishkan with these woods.
The redemption from Mitzrayim is the root of all other redemptions. Therefore, in our present exile, we must also remember that we won't be in galus forever. The time will come when we will be redeemed. This also applies to a person's personal galus, each person with his own pekel. He must know that the tzaros won't continue forever. Better times will come. This awareness helps people have the strength to endure the hardships that they go through.
Tikunei Zohar (13a) says that three matters resemble one another. Whatever is in one of them is in all three. They include Creation, the Mishkan, and every Yid. The Divrei Yisrael (תחשים ועורות ה"ד) explains that there were gold and silver in the Mishkan, and there is gold and silver in every Yid. Silver represents love, and gold represents fear, and these traits are in every Yid, for he loves and he fears Hashem. Similarly, everything that was in the Mishkan, in some way, is in every Yid.
However, the Divrei Yisrael writes that he sought to understand how there is a תחש (the animal whose skins were used to cover the Mishkan) in every Yid. He answers that Rashi (25:5) writes, "The tachash is an animal, and it was only לשעה, for a short time. It had many colors. This is the reason Targum Onkelos calls it סַס ְגוֹנָא, for it was שָׂשׂ, happy and proud of its colors." סַס ְגוֹנָא is comprised of two words: סס, which is like שָׂשׂ, happy. And גוֹנָא means colors (in Aramaic). This describes that this animal was proud of its colors. גוונא can also mean "ways". Divrei Yisroel explains that the Jewish nation is happy with the way Hashem leads them because they know that it is for the good.
Rashi adds, לשעה אלא היתה ולא. Literally, this means that the tachash only existed for a short time. It was created so the Yidden could build a Mishkan, and then it became extinct. But we can also say that there is a hinted message in Rashi's words, אלא היתה ולא לשעה. It means that a person should accept the שעה, the time and situation that Hashem gives him, no matter what it is.
As it states (Avos 4:1) בחלקו השמח עשיר איזהו, who is wealthy? Someone who is happy with his portion." Rashi writes בחלקו means "בחלק, the portion Hakadosh Baruch Hu gave him, whether it is good or bad, whether a lot or a little. He accepts everything with a good eye."
This person isn't השעה את דוחק, trying and waiting for the times to change. He is happy with the time as it is now. With these ideas in mind, a person can be happy in this month of Adar, the month when it is extra important to be b’simcha. Sadness is when one lacks emunah and doesn't believe that everything is for the good. Emunah is the root of being happy, as the Sfas Emes (Succos 5645) writes, שמחה אין 'בה הבוטח כשמחת, "No joy compares to the joy of trusting in Hashem."
Similarly, the Divrei Yisrael explains the pasuk (Tehillim 19:9) לֵב מְשַׂמְּחֵי יְש ָׁרִים 'ה פִּק ּוּדֵי, "The mitzvos of Hashem are upright, gladdening the heart." The Divrei Yisrael explains that פִּק ּוּדֵי means lacking, חסרון. (As in Bamidbar 31:49, ַדנִפְק וְלֹא אִישׁ מִמ ֶּ נּוּ, "not a man of us is missing.")
The pasuk is saying 'ה פִּק ּוּדֵי, a person must believe that what he lacks is from Hashem, and Hashem's ways are always יְש ָׁרִים, straight and good. These thoughts are לֵב מְשַׂמְּחֵי; they bring joy to people’s hearts.
Therefore, Chazal's lesson, that we be happy in Adar, is for every Yid, no matter what he is going through. How can he be happy if he is going through very hard times? Remember this lesson. Remember that everything is from Hashem, Who loves us and only bestows kindness on us. Remember that Hashem is leading us in the very best way, and remember that the situation will pass, it is only לשעה, and then everything will become good again. Remember all of this, and it is possible to be happy in Adar and throughout the year.