The Rebbe expresses joy upon hearing of the recipient’s Torah studies and conveys a blessing, following the tradition of his father-in-law, that they grow to be a Yarei Shamayim, Chassid, and Lamdan. He encourages diligence in prayer and mitzvah observance and requests updates on their progress.
https://www.torahrecordings.com/rebbe/004_igros_kodesh/kislev/836