Luther commenting on I Peter 4:12 (“Beloved, think it not strange concerning the fiery trial which is to try you, as though some strange thing happened unto you”):
...Scripture is wont to say about suffering that it is like an oven full of fire and heat...In agreement with this custom St. Peter says here that we should not be surprised or think it odd and strange when heat or glowing fire come upon us to try us as gold is melted in fire.
When faith begins, God does not forsake it; He lays the holy cross on our backs to strengthen us and to make faith powerful in us. The holy Gospel is a powerful Word. Therefore it cannot do its work without trials, and only he who tastes it is aware that it has such power. Where suffering and the cross are found, there the Gospel can show and exercise its power. It is a Word of life. Therefore it must exercise all its power in death. In the absence of dying and death it can do nothing, and no one can become aware that it has such power and is stronger than sin and death. Therefore the apostle says “to prove you”; that is, God inflicts no glowing fire or heat—cross and suffering, which make you burn—on you for any other purpose than “to prove you,” whether you also cling to His Word.
From "Sermons on the 1st Epistle of St. Peter" by Martin Luther (Vol. 30, p. 126, Luther's Works, Concordia Publishing House, St. Louis, 1967).