In a more general sense, one can hear the message of a person without the person being there at all, like when one sends a letter or gives over a message through a messenger. Thus, one can hear a message from someone from a great distance, without ever coming close to the originator of the message.
For example, a king is usually hidden in his palace, and only his decrees are heard throughout the country. Until recent times, most people in a country never saw what their king looked like at all, and only “heard” his decrees. This adds to the sense of mystery and awe from the people to the king.
We see that the idea of “hearing” in contrast to “seeing” implies distance, and distance can create awe, in the case of a king or important person.
As it is written (Chavakuk 3:2): “Hashem, I heard a report of You, and I became afraid.”
Rashi explains that the report Chavakuk the prophet “heard” was that Hashem punishes the wicked, like He punished Pharoh. He was afraid that Hashem would allow the wicked Nevuchadnetzar to rule the world because of the people’s sins. The Alter Rebbe is interpreting the verse to mean that because he “heard” about Hashem from afar, this caused him to fear Hashem.
Since fear is a result of distancing, which comes from “the left hand that pushes away,” i.e., the attribute of Gevurah-Severity. Because the person puts himself down and tells himself: “For who is it who pledged his heart to approach Hashem?” (see Yirmiya 30:21). This causes that there should come in his heart fear and awe of Hashem.
The person feels that he is not worthy to approach Hashem in prayer and experience His Light. He thinks about the distance between him, a finite and imperfect creation, and Hashem, the Infinite and perfect Creator of all existence.
