The following is an excerpt from a letter of John Berridge to a fellow minister who had recently injured himself in a bad fall.
Dear Sir,
I received your letter, and dare not say that I am sorry for your fall, nor indeed for any afflictions that God lays on His children; they are tokens of His fatherly love, and needful medicine for us. Rather would I pray that while God keeps you in the furnace, you may be still, and feel your dross and tin being purged away.
The Lord Jesus gives me a dose of this medicine most days; and I am never so well as when I am taking it, though I frequently make a crooked face at it. If your heart is as my heart, it will need many a bitter potion to cleanse and strengthen it! Afflictions have been to me some of my greatest mercies.
No lasting gain do I get, but in a furnace. Comforts of every kind make me either light or lofty, and swell me, though unperceivably, with self-sufficiency. Indeed, so much dross, native and acquired, is found in my heart, that I have constant need of a furnace. Jesus has selected a suitable furnace for me, not a hot and hasty one, which seems likely to harden and consume me–but one with a gentle and lingering heat, which melts my heart gradually, and lets out some of its dross. Though I cannot love the furnace, yet the longer I live, the more I see of its need and its use. A believer seldom walks steadily and brightly, unless he is well-furnaced.
“I have refined you, but not as silver is refined. Rather, I have refined you in the furnace of affliction!” Isaiah 48:10
May the Lord water your soul and your vineyard, and teach you to know nothing, and preach nothing but Jesus Christ!
For His sake, I am your servant,
John Berridge, 1761
The Fight of Faith 