This discourse, said by the Rebbe on the eve of Rosh Hashana in the autumn of 1972, discusses the rule that when Rosh Hashanah falls on Shabbat, one does not sound the Shofar. The Talmud says this is to avoid the possibility of someone inadvertently carrying the Shofar in the public thoroughfare on Shabbat.  

Chassidic teachings explain a further dimension of meaning: the special power of Shabbat compensates for the lack of the Shofar. But it becomes even more important to focus on the ten verses about the Shofar which are included in the Musaf prayer.