We find an allusion to the Misva of Shofar in Parashat Nisavim, where the Torah warns, Pen Yesh Bachem Shoresh Poreh Rosh Velaana Lest there is among you a root of evil of rebellion (Debarim 29:17). The first letters of the phrase, Shoresh Poreh Rosh Velaana are Shin, Peh, Resh and Vav the letters of the word Shofar.
This allusion is very significant, as it expresses the unique power and impact of the Shofar blowing namely, its ability to eliminate the root of evil within us. Before Adams sin in Gan Eden, evil was separate from good; the human being was pure and good, and evil existed outside of him. But as a result of Adams partaking from the forbidden tree, evil became ingrained within him, and since then, the good and evil inside us struggle with one another. The Shofar blowing, however, has the power to subdue the force of evil inside of us, so we can once again become perfectly good and pure. It eliminates the Shoresh Poreh Rosh Velanaa the root of evil and rebellion from which sin grows.
This power of the Shofar sound is expressed in the number of sounds that we blow. The primary obligation of Shofar blowing requires blowing thirty sounds, which we do before Musaf. We blow additional sounds during Musaf, but the primary obligation is fulfilled through the first thirty sounds. The reason for the thirty sounds is because the Torah mentions three times the obligation to sound a Terua, and the Sages inferred from the text that every Terua must be preceded and followed by a Terua. Therefore, in principle, we should blow nine Shofar sounds blowing three times a series of Tekia, Terua, and another Tekia. However, the Talmud records three different opinions as to what the Torah means by the word Terua. One view maintains that this refers to what we call a Terua a series of very short sounds whereas another opinion is that it means a Shebarim three medium-sized sounds. According to the third view, the Biblical term Terua refers to a combination of a Shebarim and Terua (Shebarim-Terua). In order to satisfy all three opinions, we blow all three Terua sounds. It thus emerges that we blow thirty sounds: three sets of Tekia-Shebarim-Terua-Tekia (3X4=12); three sets of Tekia-Shebarim-Tekia (3X3=9); and three sets of Tekia- Terua-Tekia (3X3=9) for a total of 30 (12+9+9).
The Gemara establishes that the Terua sound however it is defined must be at least the length of nine Trumitin brief sounds. Moreover, the Tekia must be the same length as the Terua. As such, when we blow thirty Shofar sounds, we blow 270 Trumitin (30X9). This number is the Gematria (numerical value) of the word Ra evil. By blowing these 270 sounds, we subdue the forces of Ra within us so our innate goodness can prevail.
Of course, our primary intention when we hear the Shofar is to fulfill the Torah obligation to hear the Shofar on Rosh Hashanah. However, we should be aware of the fact that there are many profound ideas and powers associated with this previous Misva, and that it gives us the spiritual strength that we need to subjugate our evil inclination and allow the goodness within us to shine.