Why did the sound of the Shofar begin softly, and became louder and louder?
Rashi #1: This was unlike a person 1 who sounds a Shofar; initially the sound is strong, and it weakens.
Rashi #2: It was initially soft to give the people a chance to adjust to the loud sound. If not, they would not have been able to bear it.
I.e. so the people would know that they are hearing a Divinely produced sound. (PF)
What is the Pasuk referring to when it writes "Moshe Yedaber veha'Elokim Ya'anenu v'Kol"?
Rashi and Ramban #1 (citing the Mechilta): It is referring to the last eight of the Aseres ha'Dibros, 1 which Moshe conveyed to Yisrael - with the help of Hakadosh-Baruch-Hu, who amplified his voice.
Ramban #2: It was on the third day, when Hashem descended upon Har Sinai, that Moshe took Yisrael to the foot of the mountain, whilst he ascended to a point short of the top 2 where the Shechinah was encamped, from where he instructed Yisrael (who did not understand what Hashem was saying) what to do (See Pasuk 21). 3
Ramban #3: Others explain that Yisrael were terrified of the increasing tone of the Shofar, 4 so Moshe instructed them to concentrate on what they were about to hear and Hashem responded with the Voice.
Rashbam: Moshe spoke quietly to Hashem, and Hashem spoke to him in a loud Voice, in order to override the tone of the Shofar which was increasing in strength.
Moshav Zekenim citing R. Yehudah ha'Chasid: Moshe said what he thinks that Hashem wants to say (for he understand when Hashem said al the Dibros at once), and Hashem said in more detail. E.g. Moshe said 'Lo Sisa', and Hashem said "Lo Sishba'u".
Seeing as they heard the first two Dibros from Hashem directly (Rashi).
It was only after Matan Torah that he entered the thick cloud at the top of the mountain (Ramban).
Moshav Zekenim (20:1): This enabled both of them to be heard.
Riva, citing Tosfos Brachos 45a DH b'Kolo: How can we learn from there? Hashem read and Moshe translated! Rif - Moshe needed to speak loudly, for all of Yisrael to hear. Hashem could speak softly, for only Moshe needed to hear Him. Hashem spoke as loud as Moshe, lest the translator be louder than the reader. Moshav Zekenim (20:1)