By the Grace of G-d 13th of Kislev, 5736 Brooklyn, N.Y.
Mrs.
Blessing and Greeting:
In reply to your letter, let me, first of all, remind you that there is a psak-din to the effect that nothing stands in the way of Teshuva.1 And just as a Jew is obligated to have faith in all the Mitzvos of the Torah, so is a Jew obligated to have faith in also the Mitzva of Teshuva and you have done T[eshuva] long ago.
Secondly, the Torah commands a Jew to serve G-d with joy,2 which means that a Jew is expected to be in a state of joy all the time. Indeed, if all Mitzvos must be carried out with joy, how much more so the Mitzva of Teshuva which brings a Jew closer to G-d than ever, and it comes with the assurance that "nothing stands in the way of Teshuva."
Thus, the Alter Rebbe explains in the Tanya at length3 that if a Jew feels sad or depressed, it is a sure sign that this is the work of the yetzer-hara, which uses all sorts of tricks to detract a Jew from his purpose in life, which is to serve G-d with joy. Yet, this itself can serve as a moral lesson: If the yetzer-hara tries so hard to carry out its duty of distracting a Jew from his purpose, how much more determined should a Jew be not to allow himself to be distracted in order to fulfil G-d's Mitzvos wholeheartedly and with gladness of heart.
Hoping to hear good news from you,
With blessing,
Notes and sources
1) Mishneh Torah, Hilchos Teshuvah 3:14
2) Tehillim 100:2.
3) Chapter 26 (32b) ff.
Source: Photocopy of original
Published: Teshura (Margolin-Kremer, 23 Elul, 5774).