Martin Luther, writing on Psalm 118:1 (Give thanks to the Lord for He is good, for His mercy endures forever) offers this reflection:
God proves beyond a shadow of a doubt that He is good and merciful. His daily and continual goodness shows this in rich and powerful ways. This psalm says, "His mercy endures forever." In other words, God always does what is best for us.
From "Faith Alone," July 11 devotion