Three parties speak in this Psalm: the witness for God, the brother in peril, and God Himself.
I. The witness for God, the sympathising friend of the party exposed to danger, speaking from his own experience, declares generally, "He that dwelleth in the secret place of the Most High shall abide under the shadow of the Almighty" (Psalms 91:1, and see also Psalms 91:9). Three lessons are taught in that inner school: (1) That God is true, true to Himself and true to you. (2) In your new dwelling-place you see the reward of the wicked. (3) You learn that there are members of the family not involved in your peril who yet are deeply and affectionately interested in your safety: "He shall give His angels charge over thee," etc.
II. The second party in this discourse and dialogue the brother in peril says very little. But the little which he does say is very comprehensive: "I will say of the Lord, He is my refuge and my fortress, my God; in Him will I trust" (Psalms 91:2). It is a prompt response to the very first appeal made to him. It is the language not of faith only, but of love.
III. What God Himself is overheard to say at the close of the Psalm is the glorious corner-stone of this edifice of confidence. (1) Mark the cause assigned by the Lord for the warm interest which He feels in His servant thus exposed: "He has set his love upon Me; he has known My name." (2) Mark how the Lord speaks, connecting His servant's love to Him and knowledge of His name with His own purpose of deliverance and exaltation, as if His honour were concerned to make it plain that the love is not misplaced: "I will deliver him." (3) Mark what the Lord expects on the part of His servant: "He shall call upon Me." (4) Mark the assurance of the Lord's gracious interposition, answering to His servant's calling upon Him: "He shall call upon Me, and I will answer him," etc. (5) Nor is it to be all trouble with the man of God while he is fighting the good fight and finishing his course. Nay, there is so much enjoyment for him as to make him rather wish for its continuance, and welcome the concluding promise which he hears the Lord giving: "With long life will I satisfy him, and show him My salvation."
R. S. Candlish, The Gospel of Forgiveness,p. 227.
References: Psalms 91:3. Spurgeon, Morning by Morning, p. 24.Psalms 91:5. C. Kingsley, Discipline, and Other Sermons, p. 198; Spurgeon, Evening by Evening, p. 113.Psalms 91:5-10. R. Lee, Sermons, p. 44.Psalms 91:9. Spurgeon, Morning by Morning, p. 58. Psalms 91:11. Ibid., My Sermon Notes: Genesis to Proverbs, p. 157. Psalms 91:12. H. Melvill, Sermons on Less Prominent Facts, vol. ii., p. 170.