The ultimate purpose of God in our weakness is to glorify the kind of power that moved Christ to the cross and kept him there until the work of love was done. Paul said that Christ crucified was foolishness to the Greeks, a stumbling block to the Jews, but to those who are called it is the power of God and the wisdom of God (1 Cor. 1:23f).
The deepest need that you and I have in weakness and adversity is not quick relief, but the well-grounded confidence that what is happening to us is part of the greatest purpose of God in the universe - the glorification of the grace and power of his Son - the grace and power that bore him to the cross and kept him there until the work of love was done. That's what God is building into our lives. That is the meaning of weakness, insults, hardships, persecution, calamity.
-John Piper, taken from Be Still, My Soul: Embracing God's Purpose and Provision in Suffering