The unrighteous nations are in great peril before the judgment of God. Because I am doing something in your days - You would not believe if you were told. But Judah herself is not exempt from judgment. The wickedness and idolatry of some is about to be tried in the wrath of the Babylonian invasion. There are two crucial truths in this verse that are relevant for Paul's argument.
Rescue depends on faith.
One is that rescue from the judgment of God depends on faith. That is, it's by faith that you gain your life. By faith you will not be swept away utterly in the wrath of God. By faith you will live. And that is tremendously important for Paul's point in verse 16.