The Rebbe notes Rosh Chodesh Kislev as a time of spiritual renewal, linking it to the study of Chassidus and the paths of the Rebbes. Just as the head encompasses the body, this month includes all its days, emphasizing preparation, growth, and the opening of new spiritual doors.
https://www.torahrecordings.com/rebbe/igroskodesh/016/002/5869