Psalm 91 is one of sixteen Psalms that are called Messianic Psalms; they are prophetic Psalms revealing the Messiah (Christ) to come. Psalms 2, 8, and 22 are three that you may know.
“Then Jonathan [King Saul’s son] said to the young man who bore his armor, ‘Come, let us go over to the garrison of these uncircumcised; it may be that the Lord will work for us. For nothing restrains the Lord from saving by many or by few.’ So his armorbearer said to him, ‘Do all that is in your heart. Go then; here I am with you, according to your heart.’ Then Jonathan said, ‘Very well, let us cross over to these men, and we will show ourselves to them.’” 1 Samuel 14:6-8.
“And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled in the body of His flesh through death, to present you holy, and blameless, and irreproachable in His sight…” Colossians 1:21-22.
