Already at the end of August, the morning shofar blasts sound from shuls announcing that summer is ending and Rosh Hashanah is around the corner. Every day after shacharit during the month of Ellul, the shofar is sounded. As the Mishnah Berurah explains, Ellul is a time of special love and closeness between us and God.
The 40 days from the beginning of Ellul until Yom Kippur correspond to the period when Moses was on Mount Sinai after the sin of the Golden Calf, receiving the stone tablets of the Torah for the second time.
The shofar is a call to self-awareness that rouses us to return to God at this time of special intimacy. As the Rambam puts it,the shofar says to us, "Wake up, sleepers... get up, slumberers… examine your actions, repent and remember your Creator... These are the people who forget the truth in the toils of time, and strive for years after vanities and emptiness that cannot help or save them."