The Rebbe emphasizes that for Chassidim, their unique mitzvah is spreading Chassidus, as the Rebbeim sacrificed for this mission. He encourages the recipient to strengthen his efforts, assuring it will also bring personal success. Invoking the merit of Yud Kislev, he blesses him to expand Torah and Chassidus.
https://www.torahrecordings.com/rebbe/igroskodesh/014/003/4923