The core of the sugya is Rosh Hashanah 16a, where Rabbi Yitzchak asks not why we blow shofar generally, but why the common practice is to sound the blasts twice — once while the congregation is seated and once while they stand.
Rashi (Rosh Hashanah 16b) and Tosafot (Rosh Hashanah 16b) explain the Gemara's answer, 'kedei le'arbev et haSatan,' as meaning that the repetition of the mitzvah — blowing it, then blowing it again — silences the Satan's prosecution, since he sees how beloved the mitzvot are to Israel that they perform them twice; Tosafot further cite the Arukh's reading from the Yerushalmi that the Satan fears this may be the great shofar of the future redemption.
The Ran, cited and expanded by Ran (Rosh Hashanah 3a) and Beit Yosef (Orach Chayim 585:6-8), explains that the seated blasts are the ones in question precisely because the standing blasts — those said along with the Musaf brachot — are obviously essential, and adds that the seated blasts were placed first so that people would not come to treat the essential standing blasts lightly.
Ramban likewise grounds the practice in the same Gemara passage, describing the seated blasts as occurring before Musaf with a brief brachah and the standing blasts as integrated into the order of the brachot themselves, so that the former are not merely optional but established by the Amoraim specifically to confuse the Satan.
Tur (Orach Chayim 585) and Teshuvot HaRadbaz Volume 4 1101 address a related practical question — why the congregation sits during these blasts even though the halacha generally requires standing for such mitzvot, derived from the word 'lachem' as applied to the standing required for sefirat ha'omer — and the Radbaz answers that only the blower must stand, since the essential blasts are those said with the standing brachot of Musaf, while the congregation is spared the burden of standing twice out of respect for them.
Arukh HaShulchan (Orach Chaim 585:2-3) draws together these threads, asking why the sages required blowing before Musaf at all when the essential mitzvah is fulfilled with the blasts accompanying the Musaf brachot, and answers by citing Rashi's and Tosafot's explanations of confusing the Satan side by side.
Among the Tanach sources cited by the sugya's framework, Bamidbar 29:1 and Tehillim 47:6 supply the scriptural basis for the day being called a 'yom terua' and for the shofar blast accompanying divine kingship, while Hoshea 14:3 speaks of returning to God and offering the words of one's lips in place of sacrifices, situating the shofar's role within the broader theme of teshuva that several later sources link to the practice.
Midrash Tanchuma, Vayishlach 2:3 connects the shofar of Rosh Hashanah to Israel's trembling and repentance in order to merit a favorable judgment on Yom Kippur, and Sulam on Zohar, Vayera 384 describes the shofar blast as arousing mercy that causes the Satan to lose his grip and be unable to accuse, paralleling the Gemara's language of confusing him.
Resisei Layla 36 raises a difficulty with the plain reading of the Yerushalmi's account of the Satan's alarm, asking why he would not simply know the law of blowing seated and standing, and resolves it by explaining that the Satan's confusion concerns whether the final redemption has been sealed in the hearts of the people, a matter dependent on Divine testimony rather than on knowledge of the law itself.
Teshuvot HaGeonim (Shaarei Teshuva) 65 reports that some geonic communities sounded an additional great terua after the conclusion of the prayers specifically in order to confuse the Satan, though the Geonim respond that this was not universal practice but rather something individuals undertook on their own initiative.
On the practical order of the blasts, Shulchan Arukh (Orach Chayim 592:1) records the structure of tekiot during the silent repetition of Musaf for malchuyot, zichronot, and shofarot, the very 'standing blasts' that the Gemara's sugya treats as primary.
Rav Ovadia Yosef (Maayan Omer 3:5:40) distinguishes the Musaf blasts, which require standing and are called the blasts of standing, from the earlier seated blasts whose purpose is to confuse the Satan, and adds that the blower himself must stand either because the mitzvah is inherently performed standing or out of respect for the congregation.
Tzitz Eliezer (17:27) likewise states that the shofar and terua are sounded while the congregation is seated and again while standing in order to confuse the Satan.
The Klausenberger Rebbe (Divrei Yatziv OC 257) discusses the verses connected to the shofar and cites the same teaching that the blasts are sounded both sitting and standing in order to confuse the Satan, while also noting the separate theme of proclaiming divine kingship through the shofar.
Modern poskim have also treated this sugya's deeper meaning: Nitei Gavriel, Rosh Hashana, perek 3 gives two purposes for the shofar — prompting repentance, based on Amos 3:6, and confusing the Satan — while Chiddushei Aggadot, Rosh Hashanah 16 explains that the blasts elevate the worshipers beyond the Satan's accusations, with the first set of blasts creating resistance to his power and the second, standing set completing it.
