ותוקעין ומריעין כשהן עומדין כדי לערבב השטן
and then sound again a tekia and a terua while they are standing in the Amida prayer? He answers: In order to confuse the Satan, for this double blowing of the shofar demonstrates Israel’s love for the mitzva, and this will confuse Satan when he brings his accusations against Israel before the heavenly court, and the Jewish people will receive a favorable judgment.
וא"ר יצחק כל שנה שאין תוקעין לה בתחלתה מריעין לה בסופה מ"ט דלא איערבב שטן
And Rabbi Yitzḥak said, playing on the double meaning of the word meri’in, which can mean either sound a terua or cause misfortune: Any year during which, due to some mishap, the shofar was not sounded at its beginning will suffer evil and misfortune at its end. What is the reason? Because Satan was not confused, and he was able to put forward his accusations, so that the Jewish people would be punished.
(בראשית ד, ז) לפתח חטאת רובץ ושטן מאי אמר א"ל שטן ביומא דכיפורי לית ליה רשותא לאסטוני ממאי אמר רמי בר חמא השטן בגמטריא תלת מאה ושיתין וארבעה הוי תלת מאה ושיתין וארבעה יומי אית ליה רשותא לאסטוני ביומא דכיפורי לית ליה רשותא לאסטוני
“Sin lies in waiting at the door” (Genesis 4:7), and it is no wonder that men sin. He asked him: And what did Satan the prosecutor say about their sinning? Elijah said to him: Satan, on Yom Kippur, has no license to prosecute. From where is that idea derived? Rami bar Ḥama said: The numerological value of the letters that constitute the word HaSatan is three hundred and sixty four: Heh has a value of five, sin has a value of three hundred, tet has a value of nine, and nun has a value of fifty. Three hundred and sixty-four days of the solar year, which is three hundred and sixty-five days long, Satan has license to prosecute. On the remaining day, Yom Kippur, he has no license to prosecute. Since that day is exalted above all others, there is no room for the accusations of Satan.