The furnace is a symbol of God's testing and purification of each of us. It doesn't cause only affliction, but it purifies and tests our deepest parts. We must be willing and accepting of this process, to Praise God, to See the Light it Provides and to Choose - for it does end in resurrection - to life and to death.
If we want to produce pure fruit, be firstfruits - then we must be pure. Tried by fire, tried by furnace.