I just finished reading John Piper‘s Desiring God, and was struck by this quote towards the end of the book.
The suffering of sickness and the suffering of persecution also have this in common: They are both intended by Satan for the destruction of our faith and governed by God for the purifying of our faith. (257)
This is why we hold on through difficulties. This is why we cling so tightly to the cross.
Because while it is intended for our downfall, God uses it to build and cleanse our faith.