Psalm 37:39
But the salvation of the righteous is of the Lord: He is their strength in the time of trouble.
If anyone knew what trouble was like, David did. King Saul had tried to kill him. Saul had hunted him down in the mountains. David spent years running and hiding. And yet he appreciated the strength that he received from the Lord during those difficult times. Not only did he receive physical strength, but he also got strength of mind to go on when everything seemed to be against him.