Lévitique 25:9

And thou shalt make the voice of the trumpet to sound a jubilee in the seventh month, on the tenth day of the month, on the Day of the Expiations thou shalt make the voice of the trumpet of Liberty to pass through all your land.

you will sound the horn Opinion is divided over whether the universe was created in Nisan or in Tishrey [Rosh Hashana 10b–11a]. We need not dwell on the topic, since the Exegetes have established [Rosh Hashana 27a] that we recite “This day, the anniversary of the first day of creation” in the Rosh HaShana prayer [Musaf ‘Amida for Rosh HaShana]. Moreover, we see in the current verse that one blasts the horn of the jubilee year in Tishrey — namely, toward the beginning of the year. We also have the passage “Assemble the people…” [Deuteronomy 31:12] which tells us to read the Torah during the Sukkot festival. There the verse says “…that they may hear, and that they may learn” [Deuteronomy 31:12], and it is unlikely that this should take place after half of the year has elapsed. In addition, Scripture uses such phrases as “the harvest festival, at the end of the year” [Exodus 23:16] and “at the turn of the year” [Exodus 34:22]. The definitive proof, however, is the Sabbatical year, regarding which Scripture says, “Do not sow” [:11]. Now, the sowing season in the land of Israel begins in the month of Marḥeshvan. If the year were to begin in Nisan, then we could not harvest that which we planted in the sixth year. We could not plant on the following year (because it is the Sabbatical year), and since we could not harvest what was sown in the sixth year, it would be for all practical purposes as if we could not sow for two years in a row. Scripture, however, only tells us not to sow during the seventh year. Y e hudah HaParsi said that Israel used to follow a solar calendar. If this were true, then Moshe could not have taught us the exact length of a year, concerning which even today’s astronomers have been unable to reach an agreement. Not only do we rely on our tradition, but the very etymology of the word “month” also disproves HaParsi’s thesis. The Sadducees [a derogatory reference to Karaites — Translator] claim that a “year” in our religion is a lunar year; but the term “year” does not even apply to the moon (just as the term “month” does not apply to the sun). Rather, by dividing the length of a month into the length of a year, people figured out that a year is approximately 12 months long. The remainder from this division was divided into the length of a lunar month, in order to calculate the fraction of a month left over, so that our months would be lunar months while our years would eventually conform to the solar year. Our Sages, of blessed memory, have accordingly transmitted to us a tradition, dating back to the times of Moshe, that the Sanhedrin must decree seven leap years in every 19-year cycle (even though the months themselves were proclaimed upon observing the new moon). The mysteries of the 19-year cycle can be derived from the science of astrology [cf. comment on Exodus 12:2].

THEN SHALT THOU MAKE PROCLAMATION WITH THE BLAST OF THE HORN ON THE TENTH DAY OF THE SEVENTH MONTH; IN THE DAY OF ATONEMENT SHALL YE MAKE PROCLAMATION WITH THE HORN THROUGHOUT ALL YOUR LAND. “Since Scripture states in the Day of Atonement do I not know that it is on the tenth day of the seventh month? Why then does Scripture state on the tenth day? [It is to teach us that] the blowing [of the Shofar] on the tenth day of the seventh month overrides the Sabbath throughout all your Land, but the blowing [of the Shofar] on the New Year does not override the Sabbath throughout all your Land, but only at the court alone.” This is Rashi’s language.
Now the Rabbi [Rashi], with his expert knowledge of the Talmud, and because it is all for him like a ready-laid table, was not concerned when he quoted Beraithoth without qualification, but they are misleading for the rest of the people [who are not as expert in the Talmud as he was]. For it is known and clear in the Gemara that all blowings of the Shofar, whether on the New Year, or the Day of Atonement [in the Jubilee year], or even [blowing] out of one’s own desire [without any intention to fulfill a commandment], are permitted on the Sabbath [by law of the Torah], since blowing [of the Shofar] is merely an art and not “work.” They used [in fact] to blow the Shofar everywhere by law of the Torah on the Sabbath of the New Year and on the Day of Atonement; and the matter of blowing the Shofar [only] at the court, was ordained by Rabban Yochanan ben Zaccai after the Temple was destroyed. This was decreed [by Rabban Yochanan ben Zaccai], because they [the Sages] prohibited the blowing of the Shofar [if the New Year fell on a Sabbath]. Since everyone is obliged to blow the Shofar [or to hear it blown, but not everyone is expert in it, thus we fear that] perhaps he will take the Shofar in his hand and go to an expert to learn, and thus he will carry it the distance of four cubits in a public thoroughfare [which is forbidden by law of the Torah on the Sabbath]; and Rabban Yochanan ben Zaccai therefore only permitted us to do it at the court [where the fear of the judges ensures that nobody will violate the Sabbath on account of the blowing of the Shofar]. There is thus no basis whatsoever for this prohibition in Scripture [and so how could Rashi interpret the verse before us on the basis of this Rabbinic enactment]? …

שופר תרועה, as an expression of joy over the liberation of the slaves and the restoration of lands whose sale had been forced by economic necessity to its original owners or their heirs.