# his work will be revealed
"God will show everyone what the builder has done"
# for the day will reveal it
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.
# For it will be revealed in fire. The fire will test the quality of what each one has done
"God will use fire to show the quality of his work"