The Rebbe urges the recipient to reject melancholy, emphasizing the Baal Shem Tov’s teaching on serving Hashem with joy, especially for those immersed in Torah and prayer. He cites Zohar on the power of a joyful countenance and encourages internalizing this mindset in daily life. He concludes with blessings for complete healing and good news.
https://www.torahrecordings.com/rebbe/igroskodesh/014/005/5167