Psalm 91 is without attribution in the Hebrew Masoretic Text. The Greek Septuagint version adds a superscription saying that the psalm is "of David." We should note a thematic connection between the previous psalm and this one. Psalm 90 begins with the words, "Lord, You have been our dwelling place in all generations" (verse 1). This psalm begins, "He who dwells in the secret place of the Most High shall abide under the shadow of the Almighty" (Psalms 91:1 Psalms 91:1He that dwells in the secret place of the most High shall abide under the shadow of the Almighty.
American King James Version×; compare verse 9). The Zondervan NIV Study Bible refers to Psalm 91 as "a glowing testimony to the security of those who trust in God—set beside Psalm 90 as a counterpoint to the dismal depiction of the human condition found there" (note on Psalm 91).
The first two verses present four different designations for God: Elyown ("Most High"); Shaddai ("Almighty" though perhaps meaning All-Nourishing or All-Sufficient as the root shad means "breast"); Yahweh (translated "the Lord" but meaning "He Is That He Is," signifying Eternal, Ever-living or Self-Existent); and Elohi ("My God" or "My Strong One"). These distinctions communicate various aspects of God's nature. Note in verse 14 that God sets on high those who have known His name—not referring to Hebrew pronunciation but to understanding who He is and what He is all about, which His names help to reveal. (Many people have been led to believe that there is a single sacred Hebrew name for God that must always be used when addressing Him, a doctrine that contradicts what the Bible reveals. For more on this, see "The Sacred Name—Is a Christian Required to Use It?".)
Dwelling "in the secret place of the Most High" (verse 1) recalls David's words in Psalms 27:5 Psalms 27:5For in the time of trouble he shall hide me in his pavilion: in the secret of his tabernacle shall he hide me; he shall set me up on a rock.
American King James Version×and Psalms 31:20 Psalms 31:20You shall hide them in the secret of your presence from the pride of man: you shall keep them secretly in a pavilion from the strife of tongues.
American King James Version×, which mention God hiding His people in the secret place of His presence within His tabernacle or pavilion. Abiding "under the shadow of the Almighty" (Psalms 91:1 Psalms 91:1He that dwells in the secret place of the most High shall abide under the shadow of the Almighty.
American King James Version×) is related to verse 4: "And He shall cover you with His feathers, and under His wings you shall take refuge." This is a figurative picture of God as a mother bird sheltering its young—imagery found elsewhere in David's psalms (Psalms 61:4 Psalms 61:4I will abide in your tabernacle for ever: I will trust in the covert of your wings. Selah.
American King James Version×; Psalm 63:7). As noted before, the word for "wings" can also denote "skirts" or the borders of a garment—with the imagery of a man taking a woman under his wing as symbolic of marriage (see the Beyond Today Bible Commentary on Ruth). It is likely that parent-child and husband-wife metaphors are being blended in these various references to show the great care God has in protecting His people—as the imagery is also blended with the idea of God being the defensive refuge and fortress of His people (compare Psalms 61:3-4 Psalms 61:3-4  For you have been a shelter for me, and a strong tower from the enemy.  I will abide in your tabernacle for ever: I will trust in the covert of your wings. Selah.
American King James Version×; Psalms 91:2 Psalms 91:2I will say of the LORD, He is my refuge and my fortress: my God; in him will I trust.
American King James Version×, Psalms 91:4 Psalms 91:4He shall cover you with his feathers, and under his wings shall you trust: his truth shall be your shield and buckler.
American King James Version×). Psalms 91:3 Psalms 91:3Surely he shall deliver you from the snare of the fowler, and from the noisome pestilence.
American King James Version×says God will deliver His people "from the snare of the fowler"—that is, traps laid by bird catchers (see also Psalms 124:7 Psalms 124:7Our soul is escaped as a bird out of the snare of the fowlers: the snare is broken, and we are escaped.
American King James Version×)—again comparing God's people to young birds.
The psalmist goes on to explain various ways that God's people will be kept from harm. It is important to focus on this and hold tight to the scriptural promises here. However, we must recognize that while God's people have His certain promise of protection, this does not mean that no harm of any kind will ever come to them in this life. Note verse 7, where thousands will fall around you but you yourself as a servant of God will not be touched. This has often been the experience of God's people, just as declared here. But the verse does not say that God's people will never be touched by peril or death. Verse 10 should be understood in the context of verse 7—that when many around God's people fall, they will be spared. Here, too, it is not stated that no calamity will ever befall those who serve God. The psalm itself points out that they will experience trouble in life (verse 15). Consider what happened to Job, David, Paul and others—and even to Jesus Christ, the quintessential righteous person.
Verses 11-12 say that God has commissioned His angels with protecting His people—that they will carry you through life "lest you dash your foot against a stone." So do God's people never stub their toes? That is not what is meant here. It does not say, "...so that you will never dash your foot against a stone." Rather, the point is that God's angels often intervene to protect us, sometimes even from seemingly minor harm. In the monumental confrontation between Jesus and Satan prior to the start of Jesus' ministry, the devil resorted to quoting Scripture, twisting it to suit his aims. And he chose these verses among others to make his challenge. He told Jesus to throw Himself from the pinnacle of the temple because Psalms 91:11-12 Psalms 91:11-12  For he shall give his angels charge over you, to keep you in all your ways.
 They shall bear you up in their hands, lest you dash your foot against a stone.
American King James Version×promised that God's angels would be there to catch Him (Matthew 4:5-6 Matthew 4:5-6  Then the devil takes him up into the holy city, and sets him on a pinnacle of the temple,  And said to him, If you be the Son of God, cast yourself down: for it is written, He shall give his angels charge concerning you: and in their hands they shall bear you up, lest at any time you dash your foot against a stone.
American King James Version×). Jesus countered, "It is also written, 'Do not put the Lord your God to the test'" (verse 7, NIV)—quoting Deuteronomy 6:16 Deuteronomy 6:16You shall not tempt the LORD your God, as you tempted him in Massah.
American King James Version×, referring to the negative sense of challenging God's grace. Clearly God's promise of protection does not mean that we may arrogantly presume on His favor through trying to set the terms of how He must intervene for us (by deliberately placing ourselves in harm's way).
Besides helping us to better understand Psalm 91, Jesus' response teaches us something else about comprehending the Bible in general by His words "it is also written." We should not base our understanding of a biblical subject on just one or a few verses when there are others that bear on the matter. Rather, we are to consider all of the verses that bear on a matter and deduce the truth from the whole of pertinent Scripture.
With all this in perspective, let's notice more specifically what Psalm 91 tells us. Verse 3 does not say that we will never fall into an enemy trap or experience deadly illness. Yet we can take confidence that God says here that He will deliver us from these. Sometimes this means keeping us from them (perhaps most of the time), but it may mean rescuing us after a period of affliction. And at times ultimate deliverance—salvation—is in view. Even if we should die, God will later resurrect us to be utterly impervious to harm, just as He is.
Verses 5-6 do not say that we will never experience terrifying situations, disease or devastation though He often spares us from these. But when these do come, confidence in God's care and His overall plan will help us to not "be afraid"—that is, to not live in fear. Even this does not mean that we will never go through doubting moments of worry and fright. Rather, the idea is that, if we earnestly seek God, our lives will not be characterized by fear but by faith (compare Psalms 94:19 Psalms 94:19In the multitude of my thoughts within me your comforts delight my soul.
American King James Version×).
In the concluding verses, God Himself speaks within the words of the psalm (Psalms 91:14-16 Psalms 91:14-16  Because he has set his love on me, therefore will I deliver him: I will set him on high, because he has known my name.
 He shall call on me, and I will answer him: I will be with him in trouble; I will deliver him, and honor him.
 With long life will I satisfy him, and show him my salvation.
American King James Version×). Verse 15 assures us that He will answer our prayers and that, whatever troubles do befall us, He will be with us in them—helping us to endure them. Moreover, we see again here that God will deliver us (verses 14-15), if not immediately then over time—and certainly when we are later resurrected to be in His Kingdom. "Long life" and "salvation" in the final verse applies most fully to that future time. God often does bless His people with longevity and deliverance in this life, but consider that Jesus Christ, the most righteous person to ever live, died at age 33. The ultimate long and satisfying life is that which is still to come—in contrast to the brevity and sorrow of life today as presented in Psalm 90.