What is the significance of the fact that they removed their ornaments?
Ramban #1: Whereas before they had removed some of their ornaments due to their state of mourning, now they removed them all. 1
Ramban #2 (according to the Midrash Rabah) 2 : It implies that Yisrael now accepted death upon themselves - a great source of Teshuvah.
How could they remove their ornaments? Pasuk 4 says that they did not don them!
Sifsei Chachamim: Whereas before they only removed them temporarily, in the way of mourners; now they removed them permanently.
Rosh: Pasuk 4 means that they did not put the Aveilus on their hearts 2 ; each man still wore his ornaments. Moshav Zekenim (4) - the note under v'Lo Shasu is Tevir, to show that it is not read with 'Ish'. Hadar Zekenim - also Targum Yerushalmi 3 supports this - "Lo Shavi'u Al Libhon."
Moshav Zekenim (4): Everyone received two crowns when they declared "Na'aseh v'Nishma", and removed Edyo (one) by himself (Pasuk 4). Hashem commanded them to remove Edyam (also the other), and they did so.
Riva citing R"M of Kutzi: Edyam was the blood of the Bris that was on their garments. The Chachamim removed it by themselves; after Chet ha'Egel; Hashem now commanded everyone to remove them.
Riva: Yisrael removed by themselves, but Moshe did not. Hashem now commanded Moshe to remove, lest Yisrael be depressed.
Da'as Zekenim (5), Hadar Zekenim: Verse 4 teaches that temporarily they did don them, but they expected to keep them. Hashem said that they will be removed absolutely. 4
Da'as Zekenim (5, citing R. Yosef Karo): In verse 4, Edyam are the prized clothes that they wore at Matan Torah. In verse 5-6, they are the crowns that they received.
See also Sifsei Chachamim.
Stnadard Mikra'os Gedolos do not have Targum Yerushalmi on our verse, and Targum Yerushalmi of Neofiti does not say so. (PF)
Hadar Zekenim: This is difficult, for "Hored" connotes removing what one is wearing!
What happened to the ornaments that Yisrael removed?
Why does it say "va'Yisnatzlu" (passive)?