We find an allusion to the Misva of Shofar in Parashat Nisavim, where the Torah warns, "Pen Yesh Bachem Shoresh Poreh Rosh Ve’la’ana" – "Lest there is among you a root of evil of rebellion" (Debarim 29:17). The first letters of the phrase, "Shoresh Poreh Rosh Ve’la’ana" 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 Adam’s 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 Adam’s 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 Ve’lana’a" – 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 "Teru’a," and the Sages inferred from the text that every Teru’a must be preceded and followed by a Teki'a. Therefore, in principle, we should blow nine Shofar sounds – blowing three times a series of Teki’a, Teru’a, and another Teki’a. However, the Talmud records three different opinions as to what the Torah means by the word "Teru’a." One view maintains that this refers to what we call a Teru’a – 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 Teru’a refers to a combination of a Shebarim and Teru’a ("Shebarim-Teru’a"). In order to satisfy all three opinions, we blow all three Teru’a sounds. It thus emerges that we blow thirty sounds: three sets of Teki’a-Shebarim-Teru’a-Teki’a (3X4=12); three sets of Teki’a-Shebarim-Teki’a (3X3=9); and three sets of Teki’a- Teru’a-Teki’a (3X3=9) – for a total of 30 (12+9+9).
The Gemara establishes that the Teru’a sound – however it is defined – must be at least the length of nine "Trumitin" – brief sounds. Moreover, the Teki’a must be the same length as the Teru’a. 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.