The month of Elul, in Jewish tradition, is the month of return. The shofar is blown every morning in synagogues around the world, and propitiatory prayers — selichot — are recited twice a day. The custom has a precise origin story, and it runs through the sin of the Golden Calf.
Moses Goes Up for the Second Tablets
After Israel had worshiped the molten calf and Moses had shattered the first tablets (Exodus 32:19), the Holy One told him to ascend Mount Sinai a second time to carve and receive new tablets. The Sages identify this command as coming at the beginning of the month of Elul.
"Go up to Me on the mountain," the Holy One said. Moses went up. And forty days later — on the tenth of Tishrei — he descended with the second set of tablets, the sign that the Holy One had forgiven Israel for the calf.
That tenth of Tishrei became Yom Kippur, the Day of Atonement, for all future generations.
The Trumpet in the Camp
Before Moses ascended that second time, the Sages say, he ordered the shofar to be sounded throughout the camp — a public signal that the forty days of repentance had begun, that no one should draw near the mountain, and that the whole community should turn its heart.
This is the origin of the practice, still kept today, of sounding the shofar in the synagogue every weekday morning of Elul. From the second of Elul until the eve of Yom Kippur, propitiatory prayers are recited morning and evening, and the shofar blasts the ear awake.
The forty days match the forty days Moses spent on Sinai reconciling Israel with the Holy One. Every year, Jews re-walk those forty days together — climbing the same mountain of return.