Rashi: It is a Kli used to refine silver. Kor is used to purify gold. Malbim - because gold is dearer than silver, a Kor is needed to purify it. It has a bigger fire than a Metzaref. Impurities do not leave gold as easily as they leave silver. Also, because gold is dearer, there is more adamancy to remove even tiny impurities.

Rashi: Man is refined and esteemed according to his praise - that people praise him for his good deeds. The Rabim test if he is good or bad.

Sha'arei Teshuvah 3:148: A person's level is according to what he praises. If he praise good deeds, Chachamim and Tzadikim, know he is good and the source of Tzedek is in him. His heart praises the good in all his ways, and he debases Aveiros and disgraces those who do them. Even if he might have hidden sins, he loves Tzedek, and has a root in [proper] choice. He is among those who honor Hashem. One who praises lowly deeds or Resha'im, he is an absolute Rasha and profanes Avodas Hashem.

Malbim: Just like because gold is dearer, there is more adamancy to remove even tiny impurities, a man is refined according to his praise. The more praised that he is, there is more adamancy about tiny impurities. Shogeg sins of a Chacham are considered like Mezid. A Chacham is refined via fire and afflictions more than average people.