When God puts His own people into the furnace, He keeps His eye on the clock and His hand on the thermostat. He knows how long and how much.
If we rebel, He may have to reset the clock; but if we submit, He will not permit us to suffer one minute too long. The important thing is that we learn the lesson He wants to teach us and that we bring glory to Him alone.
We may question why He does it to begin with, or why He doesn’t turn down the heat or even turn it off; but our questions are only evidences of unbelief.
Job 23:10 is the answer: “But He knows the way that I take; when He has tested me, I shall come come forth as gold” (NKJV). Gold does not fear the fire. The furnace can only make the gold purer and brighter."
(Wiersbe, W. Be Patient. An Old Testament study. Wheaton, Ill.: Victor Books)