Rav Wolbe's father-in-law, Rav Avrohom Grodzinski, makes a penetrating insight into the month of Elul. In his sefer, Toras Avraham (pg. 193), he cites the Tur (O.C. siman 581) who quotes the Pirkei D'Rebbe Elazar. "On Rosh Chodesh Elul, Hashem told Moshe to ascend the mountain in order to receive the second luchos. They sounded a shofar in the camp, "Moshe has ascended the mountain," lest the nation stray after idol worship (again). . . Therefore, Chazal initiated that every year we are to blow the shofar commencing with Rosh Chodesh Elul to warn Bnei Yisroel to do teshuva, as it is written, 'Is the shofar ever sounded in a city and the people will not tremble?'"
Rav Grodzinski comments that it is difficult to understand the trembling mentioned in conjunction with the shofar. When they were notified that they were going to receive the second set of luchos, they should have been overjoyed. Not only did this proclamation indicate that Hashem had forgiven them for the sin of the golden calf, it also heralded their receiving the entire Torah, something that even the Avos did not merit. With this in mind, where does fear and trembling fit into the picture?
He answers that Bnei Yisroel recognized the awesome joy associated with receiving the luchos, and they trembled lest they lose this intense pleasure. They already witnessed how with a single sin they fell from the pinnacle of spirituality, and they feared lest the situation repeat itself. This is the trembling associated with Moshe's ascension. Similarly, this is the fear instilled by the shofar each and every year. Elul presents an opportunity that simply cannot be missed. On Rosh Hashana Hashem apportions life, and the keys to all physical and spiritual success. On Yom Kippur, one has the ability to rid himself of a year, or even years, of transgressions. Is there a greater joy than this? One must take delight in this awesome opportunity, and tremble lest it slip through his fingers. This fear is what propels a person to do teshuva so that he, too, can gain from this treasure chest of the Days of Awe.
How does one go about doing teshuva? Rav Wolbe (Alei Shur vol. II pg. 415) cites Rabbeinu Yonah's explanation of Hillel's dictum (Avos 1, 14), "If I am not for myself, who will be for me?" Rabbeinu Yonah explains that if one does not arouse himself, no amount of mussar can help him. It is possible to listen to many mussar discourses and to read through many mussar seforim and gain nearly nothing. A person has to arouse himself by properly digesting what he has heard or read. He should take a line in a mussar sefer and see if he can relate to what is written. If his actions are not in tandem with what he has read, he must take a minute to contemplate the reason behind this laxity and if there is anything, albeit minute, that he can do to change his situation.
Along with Elul comes a fear. Not a fear laced with dread, rather, a fear mixed with joy lest one lose the tremendous opportunity that is knocking on his door. Hashem has so much that He wishes to give us, we must merely arouse ourselves so that we can be worthy of receiving it.