It has become a widespread custom to sound the shofar one hundred times on Rosh Hashanah - including tekiot, shevarim and teruot. These hundred sounds are considered symbolic of the one hundred and one letters contained in the lament of Sisera's mother as she awaited her son's return from the battlefield as recorded in the Song of Devorah (Judges, 4).
The relationship of the sounding of the shofar on Rosh Hashanah and the lament of Sisera's mother bears further explanation. Furthermore, if this is the source of the custom of sounding the shofar more times than required, why do we not sound it one hundred and one times?
The purpose of the sounding of the shofar is to arouse G‑d's compassion for the descendants of Yitzchak who was offered like a ram upon the altar, whereas the lament of Sisera's mother was an expression of grief suffused with animosity and hatred. Waiting for her son to return from the battlefield, she imagined that he was busy slaughtering and taking spoils and it was through thoughts such as these that she sought to console herself. Can there be greater cruelty?
Therefore, we implore: May the one hundred shofar sounds of compassion and mercy nullify every one of those other outcries -except one: the sorrow of a mother over her son. For even the most brutal of mothers is deserving of compassion when she laments her son. Thus, we sound a hundred sounds and not one hundred and one.
Among Sephardic communities, an additional tekiah is sounded before the recital of Alenu at the end of Musaf, for a total of one hundred and one shofar sounds. This corresponds to the numerical value of the letters of the name Michael, Israel's guardian angel who seeks mercy on their behalf.
It is customary to sound a long blast as the concluding sound of the shofar in order to confuse Satan and prevent him from accusing Israel of lacking fear of Divine judgment because they eat a festive meal after the services. When Satan hears that the shofar is sounded more times than the Torah requires, he becomes confused and is apprehensive that the additional sounds might be that of the shofar of Mashiach.
But is it possible that Satan, the fearless accuser of Israel who is capable of setting clever traps for mankind, is so foolish that he is frightened of a sound that even a child knows is not the sound of the shofar of Mashiach?
We learn that when the people of Israel hear the shofar sounded on Rosh Hashanah, they are brought to a level wherein they are indeed capable of bringing about the final redemption. When they sound the shofar in fulfillment of the precepts of the day, their closed hearts are opened, they regret their sins, and their thoughts turn to repentance. Satan knows the power of the sounds of the shofar. Though they might originate from man's lips, they can well culminate with the coming of Mashiach ben David.