This can be stated in active form. Alternate translation: "God will show everyone what the builder has done" (See: [[rc://en/ta/man/translate/figs-activepassive]])
The "day" refers to the time when God will judge everyone. When God shows everyone what these teachers have done, it will be like the sun has come up to reveal what happened during the night. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Just as fire will reveal the strengths or destroy the weaknesses of a building, God's fire will judge man's efforts and activities. Alternate translation: "God will use fire to show the quality of his work" (See: [[rc://en/ta/man/translate/figs-metaphor]])