<p>to a person who felt that difficulties of the times led to a weakening in his holy work</p>
<p><a href="https://chabadlibrary.org/books/admur/ig/14/4943.htm">ספרי כ"ק אדמו"ר - אגרות קודש - כרך יד - ד'תתקמג | ספריית ליובאוויטש (chabadlibrary.org)</a></p>

Personal and Public Correspondence of The Rebbe.
In the Rebbe's correspondence one can see his scholarship, the care he has for every individual, the communal projects which he pioneered, and many other dimensions of his leadership. the correspondences deal with every aspect of life.