In a recent meditation on Psalm 91, John Piper draws out two important conclusions:
I conclude that Psalm 91 means two things about the suffering of the saints. One is that often God amazingly delivers them physically when others around them are falling. The other is that God often wills for his children to suffer, but forbids that the suffering hurts them in the end. Such evil will never befall you.
Consider how Charles Spurgeon explains this same meaning:
It is impossible that any ill should happen to the man who is beloved of the Lord; the most crushing calamities can only shorten his journey and hasten him to his reward. Ill to him is not ill, but only good in a mysterious form. Losses enrich him, sickness is his medicine, reproach is his honor, death is his gain. No evil in the strict sense of the word can happen to him, for everything is overruled for good. Happy is he who is in such a case. He is secure where others are in peril, he lives where others die. (my italics, The Treasury of David, Vol. 2, Part 2, 93)
Read the entire post, Your Executioner May Laugh You to Scorn for Quoting Psalm 91.