Teshuvah should be done with happiness. The Chasam Sofer zt'l says it is a serious aveirah to be sad while doing teshuvah. Perhaps a hint to this idea is in this week's parashah, the parashah that is always read either on rosh chodesh Elul or on the Shabbos mevorchim Elul. This is because the word שמחה is written many times in this week's parashah! (see pasukim: 12:7, 12:12, 12:18, 14:26, 16:11, 16:14, 16:15.) In Elul we do teshuvah, and the Torah hints to us that we should do so with joy.
In a letter to his son, the Beis Aharon writes, "A person must work on simchah, on being happy, more than all other good middos."
Rebbe Yechiel of Alexander zt'l teaches that the roshei teivos of (16:15) שמח אך והיית spell א"שו, which translates as "a lie". This tells us that when it comes to being happy, one may pretend that he is happy, even when he isn't. Generally, we avoid acting and pretending. A person must be honest and truthful. However, when it comes to being happy, you may pretend because pretending leads to genuine joy. א"שו is found in the roshei teivos. We can explain this because he will only need to pretend to be happy initially (like the roshei teivos are only at the beginning of the word). If he pretends to be happy at the beginning, he will be genuinely happy afterward. This is for two reasons: A person’s thoughts follow his actions. If he acts like he is happy, he will
