Rashi: It was not via Kesef, and not via fire of Gehinom. Refer to 48:10:2:1.

Radak: I refined you via afflictions of the sword, captivity and plague. It was unlike one who refines silver - he removes all impurities until only pure silver remains. I did not do so. Very few would remain if I did so! Rather, the Resha'im among you, I afflicted them with illness, captivity, death of children, animals or Peros, like it says in the curses.

Rashi: I chose for you the Kor (smelting pot) of Oni (poverty). Radak - Oni includes all kinds of afflictions.

Radak #1: Some say that Becharticha is like Bechanticha ¹ (I tested you).

Radak #2: I selected you. Refining is selecting silver from the impurities.

Malbim: One who refines impurities in a cauldron of silver, he discards the impurities for the sake of the silver. However, one who refines impurities in a cauldron of Oni, which has no silver, only poverty and impurities, he selects only the worst impurities, and leaves the esteemed metals. When I will refine you in a cauldron to remove the impurities (Resha'im), I will not remove all of them, for it is a cauldron of impurities, and no one would remain! Therefore, I will eradicate only the great Resha'im, but not the average Resha'im.