"but he himself will be saved, but as through fire" (3:15). What does that mean?

The words close what the letter says about building on the foundation. "each man’s work will be revealed. For the Day will declare it, because it is revealed in fire; and the fire itself will test what sort of work each man’s work is." (3:13). "If any man’s work remains which he built on it, he will receive a reward. If any man’s work is burned, he will suffer loss, but he himself will be saved, but as through fire." (3:14-15). In these verses the fire tests the work (3:13); the one whose work remains receives a reward (3:14); the one whose work is burned suffers loss, and is himself saved, "but as through fire" (3:15). The letter doesn't explain the words further, and these notes don't either.