I. David's refuge in the valley of the shadow of death was faith in God, the ever-near. David had entered the valley of the shadow of death of the heart. He had been betrayed, insulted, exiled, by the one whom he had loved best. It was enough to make him disbelieve in Divine goodness and human tenderness, enough to harden his heart into steel against God, into cruelty against man. In noble faith he escaped from that ruin of the soul and threw himself upon God: "I will fear no evil, for Thou art with me." This verse sprang from the heart of a Hebrew king. It has found an echo in the heart of all humanity.
II. The next verse, on the supposition that the Psalm was written at the time when David was at Mahanaim, is at once comprehensible. It is a thanksgiving to God for the blessings of friendship which were given him in his exile. One of the sad comforts of trial is that it is the touchstone of friendship. We realise then who are true gold. We often lose in trial what is calculable; we often gain what is incalculable. Precisely the same principle holds good in the spiritual world. The blessing of all trial is that it disperses the vain shows of life on which we rested, and makes Christ, the eternal certainty, more deeply known, more deeply ours as the Friend who loveth at all times.
III. The last verse combines the retrospect and the prospect of faith. David glances over his whole life, and declares that it has been very good: "Surely goodness and mercy have followed me all the days of my life." That is the expression, not of a youthful shepherd's, but of a man's, experience, and it is an expression of triumphant faith.
S. A. Brooke, Sermons,p. 71.