This can be stated in active form. Alternate translation: "God will salt everyone with fire" or "Just as salt purifies a sacrifice, God will purify everyone by allowing them to suffer" (See: [[rc://en/ta/man/translate/figs-activepassive]])
Here "fire" is a metaphor for suffering, and putting salt on people is a metaphor for purifying them. So "will be salted with fire" is a metaphor for being purified through suffering. Alternate translation: "will be made pure in the fire of suffering" or "will suffer in order to be purified as a sacrifice is purified with salt" (See: [[rc://en/ta/man/translate/figs-metaphor]])