“To be free from worry and to be free from trouble are not the same thing. Christ commands us not to be anxious, but does not promise that we will be immune to all misfortune. On the contrary, there are many indications that he knew all about calamity...
He said of the sparrows, ‘Not one of them will fall to the ground without your Father’s will.’  But sparrows do fall to the ground and get killed.  His promise is not that they would not fall, but that this would not happen without God’s knowledge and consent. People fall too...
A Christian’s freedom from anxiety is not due to some guaranteed freedom from trouble, but to the confidence that God is our Father, that even suffering is within the orbit of his care, and that ‘in everything God works for the good of those who love him, who are called according to his purpose’ (Romans 8:28).”
~ John R.W. Stott, The Sermon on the Mount