(Proverbs 27:21 KJV) As the fining pot for silver, and the furnace for gold; so is a man to his praise.
The “crucible” (4715) and the “furnace” (3564a) were two different ways of refining precious metals. They applied heat to separate the valuable from the waste product. The two metals referred to were silver and gold. Both of them could be found in a natural form that was pure enough to be shaped by pounding and pressure. It was possible to make ornaments and decorations without the heat but the metal was not as lustrous and useful as the purified product.
In the same way it is possible for us to be useful to God without being tested but the ability to live in righteousness and be salt is seriously limited without refining. Imagine yourself a gold nugget. You are happy as a pig in the mud as you lay in the dirt. Someone finds you and uses a thong to make you into a pendant. Everyone is impressed. In order to become a beautiful setting for a diamond or other jewel you find yourself crushed and heated to the point of purification. In the process you not only become more beautiful but much more valuable.
So? I don’t ever expect to enjoy the growing process but I can accept it knowing that the end results will make me a little straighter and closer to the final product God is designing.