Having already warned (in the previous Pasuk) against touching the mountain, why does the Torah see fit to repeat it?
Rashbam: The Torah is referring (not to touching the mountain, but) to touching the sinner by killing him from close quarters, 1 and fulfilling the command by throwing stones or firing arrows at him, as the Pasuk goes on to explain.
Targum Yonasan: What the Torah is saying is that One may not lay a hand on anyone who comes close to the Mountain, but that he will be stoned by hailstones or by arrows of fire.
Moshav Zekenim: This verse forbids touching (killing) one who touched the mountain. We must let Shamayim kill him.
Da'as Zekenim: This verse teaches that he is stoned. Do not say that Stam Misah is choking.
Rashbam: Because whoever kills him will then himself be Chayav Misah for committing the same sin.
What did Hashem mean when he added "O Yaroh Yiyareh"?
Rashi: This teaches us that the regular sentence of Sekilah is carried out by pushing the culprit down 1 from the area where the Sekilah takes place.
Rashbam: Refer to 19:13:1:1.
Targum Yonasan: Refer to 19:13:1:2.
Rashi: From a height of two Amos. See Beshalach, 15:4 - Rashi Sanhedrin, 45a.
What is "bi'Mshoch ha'Yovel" that permits to ascend the mountain?
Rashi #2 (Beitzah, 5b, citing the Mechilta) and Rashbam: It is when the blowing of the Shofar ceases.
Rashi in Beitzah, 5b. It is like the way of musicians to end with a long note. (This is like we do in Teki'as Shofar on Rosh Hashanah
What exactly was the "Yovel"?
Rashi: It was the Shofar that was made from the horn of Yitzchak's ram. 1
Ramban (according to Kabalah): It was the voice of Pachad Yitzchak. 2
Rashi writes that "Oh Yaro Yiyareh" teaches that one who is stoned is cast down. It says "Sakol Yisakel" before this. Beis Din casts him down before throwing stones! Within one matter, the Torah is in order (Pesachim 6b)!
Tosfos (Pesachim 6b DH Aval), Moshav Zekenim #2, Riva: Here is different, for a Drashah teaches that stoning is [written] next to death - "u'Skaltam ba'Avanim va'Mesu" (Devarim 17:5). Therefore, stoning is after casting down.
Riva, citing R. Meir Kochbi, Hadar Zekenim: The Torah needed to write Oh Yaro Yiyareh last, to teach that if he died from the fall, they were Yotzei (without stoning him). There is no need to teach that if he died through stoning, they were Yotzei.
The verse does not discuss Misas Beis Din. Refer to 19:13:152:4.
Rashi writes that "Oh Yaro Yiyareh" teaches that one who is stoned is cast down. Why does it say "Oh"? In every case he is cast down (and if this does not kill him, they stone him)!
Riva: We find that "Oh" can mean 'Asher' (that), e.g. "v'Higisho El ha'Deles Oh El ha'Mezuzah" (below, 21:6). The Targum Yerushalmi is 'to the door that is attached to the Mezuzah.' Here it means that we stone one who was cast down.
Refer to 19:13:151:3.
Hadar Zekenim: Here, "Oh" means Im (if)