I have considered the days of old, the years of ancient times. I call to remembrance my song in the night: I commune with mine own heart: and my spirit made diligent search. – Psalm 77:5,6

Going on with the strategy of war, what next? Why, in the fifth verse we read how David maintained his courage and his constancy-“I considered the days of old.” He enquired of hoary fathers, and looked back upon the inspired traditions, if I may be allowed the expression, of the early church. He wanted to see whether God ever did forsake any of his people, rightly judging that if He never did, He never would, and firmly resolving that till he could find a clear case of God’s unfaithfulness he would not yield an inch of soil, nor give up a stone of any fortress, but would hold on and fight the battle out. That inward musing helped him much. The enemy began to weary, while he recruited His strength.

But now he used another weapon. He looked to his own experience-see the sixth verse. “I called to remembrance my song in the night.” Past experience acknowledged gratefully and taken as the index of what the future will be-this is another of David’s shields and spears. And then he seemed to put a whole path of spears before the enemy, and hold up an entire wall of shields when he came to close quarters with him, and said, “Will the Lord cast off for ever? Will He be favorable no more? Is His mercy clean gone for ever? Doth His promise fail for evermore? Hath God forgotten to be gracious? Hath He in anger shut up His tender mercies?” Oh! this is how to win the battle. The next time, dear friend, you find yourself downcast in trouble, do not run away because Giant Despair is so strong. Though pressed by danger and beset by foes, feed not this frenzy of the soul with gloomy black forebodings. Armed with David’s shield and spears, attack him; show a bold front, and so shall you resist the devil and find that he flees from you, and you shall come back from the conflict with louder notes of victory than you had dreamed before. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0972.cfm