Why does the Torah add the words 'ha'Motz'im oso Mekoshesh"?
Why does the Torah repeat the (otherwise superfluous) words "Mekoshesh Eitzim"?
Sifri: To teach us that the witnesses are obligated to warn the person who is transgressing Shabbos as to which Av Melachah he is contravening.
Why did the Mekoshesh desecrate Shabbos?
Moshav Zekenim and Targum Yonasan (both on Pasuk 32): Since Yisrael had not yet been told the punishment for Chilul Shabbos, he did it in order to make a Kidush Hashem - to demonstrate practically what happens to someone who desecrates Shabbos, so that Yisrael would learn from him and not suffer the same fate. 1
Refer to 15:34:1:1 and see Oznayim la'Torah DH 'va'Yimtz'u Ish', who explains why the Mekoshesh's deed ws commendable. He also supports this explanation from the fact that, as opposed to the Megadef, the Torah twice refers to the Mekoshesh as "Ish", which is a Lashon of Chashivus - See DH 'Ish Mekoshesh'.
