You do not have your faith once and for all. The faith that you will confess today with all your hearts needs to be regained tomorrow and the day after tomorrow, indeed, every day anew. We receive from God only as much faith as we need for the present day. Faith is the daily bread that God gives us. You know the story about manna. This is what the children of Israel received daily in the desert. But when they tried to store it for the next day, it was rotten. This is how it is with all the gifts of God. This is how it is with faith as well. Either we receive it daily anew or it rots. One day is just long enough to preserve the faith. Every morning it is a new struggle to fight through all unbelief, faintheartedness, lack of clarity and confusion, anxiety and uncertainty, in order to arrive at faith and to wrest it from God. Every morning in your life the same prayer will be necessary: I believe, dear Lord, help my unbelief.
from The Collected Sermons of Dietrich Bonhoeffer (Fortress, 2012), 203.