With the Day,
Paul is referring to the day of judgment. On this day, everything that a person has done in his/her lifetime will be tested (see also Mark 9:49; Romans 2:16; 2 Corinthians 5:10; 1 Peter 1:17; Revelation 20:12).
The fire
that will test everyone’s works is not the fire of hell, nor is it a purgatory fire, as is believed in Roman Catholicism. Paul is drawing on an Old Testament usage of the image of fire (Proverbs 17:3; Isaiah 48:10; Jeremiah 6:29; Malachi 3:2–3). Just as fire tests metal, so God tests a person’s works and the motives of his heart.
To a certain extent, God tests and chastises people even in this life. However, on the day of judgment, all the works that each one
had done will be thoroughly tested. On that day, even the most secret things will be made plain for all to see (see also Luke 12:1–3).
13 each one’s work will become manifest, for the Day will disclose it, because it will be revealed by fire, and the fire will test what sort of work each one has done.