כִּֽי־עַמְּךָ֥ וְנַחֲלָתְךָ֖ הֵ֑ם אֲשֶׁ֤ר הוֹצֵ֙אתָ֙ מִמִּצְרַ֔יִם מִתּ֖וֹךְ כּ֥וּר הַבַּרְזֶֽל׃
Denn dein Volk und dein Erbe sind sie, die du herausgeführt aus Ägypten, aus dem eisernen Ofen [aus harter Knechtschaft].
Rashi
The smelting pot of iron. The earthenware30The phrase “of iron” refers to the purpose of the pot, not the material of which it is made. The pot itself is earthenware. utensils used to purify gold of its impurities is called כור.31A crucible used for melting gold.—Metzudas Tzion The oppression suffered by the Bnei Yisroel in Egypt is likened to a furnace which purifies metal, because Bnei Yisroel underwent a process of spiritual purification.