1)
Verse 18 already said that he should be clothed with a curse!
1.
Radak: The matter is repeated to strengthen it.
2.
Malbim: Here it teaches that it should be like a wide and long garment that goes over all his garments. I.e. the curse will be known and abundant.
2)
What is "Mezach"?
1.
Rashi: It is a belt. "U'Mezi'ach Afikim Ripah" (Iyov 12:21) means 'he opened a strong belt.'
2.
Malbim: It is a belt used to lift long garments, to make them fit his size. The curse is longer than his size; it should adjust itself to his size.
