Anyone who escaped one “fire” of God’s judgment would not truly be safe. Here, “fire” is a picture of severe judgment.
This first fire likely refers to the defeat of Judah by King Nebuchadnezzar of Babylon in 597 BC (2 Kings 21:1–4). Some people survived that attack and were taken into exile.
But those who escaped that disaster would soon face another one. This second fire refers to the final destruction of Jerusalem in 586 BC. In other words, escaping the first judgment would not prevent the second.