en_tn_condensed/mal/03/03.md

he will purify the sons of Levi

Forgiving the sons of Levi and persuading them not to sin any longer is spoken of as if it were purifying metal. Alternate translation: "he will correct the sons of Levi and forgive them for having sinned" (See: rc://en/ta/man/translate/figs-metaphor)

the sons of Levi

Here "sons" refers to descendants. The male descendants of Levi were the priests and workers in the temple. (See: rc://en/ta/man/translate/figs-metaphor)

He will sit

Here sitting implies the action of a metalworker, who sits down in order to purify small amounts of gold or silver. It also implies the action of a king, who sits down to judge people and give decrees. (See: rc://en/ta/man/translate/figs-simile and rc://en/ta/man/translate/figs-explicit)

He will refine them like gold and silver

Here persuading people not to sin any longer is spoken of as if a metalworker were making gold and silver more pure. (See: rc://en/ta/man/translate/figs-simile)

they will bring offerings of righteousness to Yahweh

Here "of righteousness" means "motivated by righteous desires to worship God." Alternate translation: "they will bring acceptable offerings to Yahweh in order to worship Yahweh"