Blow the shofar in the month. This is what the scripture says (Psalms 89:16): "Happy is the people who know the shofar blast; they walk, O Lord, in the light of Your countenance." "Those who know the shofar blast" refers to the generation of the wilderness who camped and traveled by the sound of the shofar, as it says (Numbers 10:4): "And if they blow but one [shofar], then the princes, the heads of the thousands of Israel, shall gather themselves unto you."
"They walk, O Lord, in the light of Your countenance" as it says (Exodus 13:21): "And the Lord went before them by day." Another interpretation: "Happy is the people" refers to the elders who determine the months and establish the new year. "In the light of Your countenance" - Rabbi Abbahu said, this refers to God who agrees with them. Rabbi Yosei ben Yaakov said in the name of Rabbi Acha (Genesis 49:21), "Naphtali is a hind let loose, who utters beautiful words."
These are the words of Torah that were given through the shofar, as it says (Exodus 20:15): "The sound of the shofar." Therefore, "Blow the shofar in the month." Rabbi Yoshiyah said, "Do not the nations of the world also have hands raised in doubt?" Rather, "Happy is the people" refers to the Jewish people who know how to please God with the shofar.
Another interpretation: "Happy is the people" refers to the Jewish people who know how to please God on Rosh Hashanah. "In the light of Your countenance they will walk" refers to Yom Kippur, on which the Lord forgives and enlightens them. "Blow the shofar in the new moon" refers to the month during which the new moon is covered, and this is Rosh Hashanah. "Blow the shofar in the new moon."
The rabbis say: "Renew your deeds and improve your deeds, and I will cover your sins," as it is said: "You have borne the guilt of Your people, You have covered all their sins" (Psalms 85:3). Rabbi Berechiah said in the name of Rabbi Abba: "Improve your deeds and renew your deeds." Just as the shofar sound comes from one end and goes out the other, so do all the accusers in the world accuse before me, but I hear from one side and vindicate from the other. Therefore, blow the shofar in the new moon."