Why does the Torah call the Choshen "Choshen Mishpat"?
Rashi #1: Because it atoned for perversion of justice.
Rashbam: Because it informs the Mishpat of Yisrael (in connection with future events that require clarification).
Seforno (Pasuk 30): Because, the Kohen Gadol wore it on his heart in order to pray on behalf of Yisrael that they should merit in judgment (before Hashem). 3
Targum Yonasan: It served the triple purpose of a. conveying to Yisrael matters that were hidden from the Dayanim; b. revealing to them war tactics; c. atoning for perversion of justice.
Having said "ke'Ma'aseh Eifod Ta'asenu", why does the Torah see fit to repeat "Zahavm Techeiles ve'Argaman ..."?
Toras Kohanim, Vayikra, 2:4: To limit the comparison to the composition of threads
Why does the Torah repeat "Ta'aseh Oso"?
Oznayim la'Torah: To teach us that the entire Choshen