Count it all joy, my brothers, when you meet trials of various kinds, for you know that the testing of your faith produces steadfastness. (James 1:2–3)
Strange as it may seem, one of the primary purposes of being shaken by suffering is to make our faith more unshakable.
Faith is like muscle tissue: if you stress it to the limit, it gets stronger, not weaker. That’s what James means here. When your faith is threatened and tested and stretched to the breaking point, the result is greater capacity to endure.
God loves faith so much that he will test it to the breaking point so as to keep it pure and strong. For example, he did this to Paul according to 2 Corinthians 1:8–9,
We do not want you to be unaware, brothers, of the affliction we experienced in Asia. For we were so utterly burdened beyond our strength that we despaired of life itself. Indeed, we felt that we had received the sentence of death. But that was to make us rely not in ourselves but on God who raises the dead.
The words “but that was to” show that there was a purpose in this extreme suffering: it was in order that Paul would not rely on himself and his resources, but on God — specifically the future grace of God in raising the dead.
God so values our wholehearted faith that he will, graciously, take away everything else in the world that we might be tempted to rely on — even life itself. His aim is that we grow deeper and stronger in our confidence that he himself will be all we need.
He wants us to be able to say with the psalmist, “Whom have I in heaven but you? And there is nothing on earth that I desire besides you. My flesh and my heart may fail, but God is the strength of my heart and my portion forever” (Psalm 73:25–26).
From John Piper’s Future Grace, page 347