What does Psalm 91:11 mean?

Every verse of Scripture needs to be understood in a proper context; God's words are not meant to be cut apart and used like talismans or magical spells. In this passage, the psalmist has celebrated the Lord's incredible ability to protect His people (Psalm 91:1–10). This is a part of God's ability, but it does not mean God absolutely guarantees the health and safety of anyone who demands it. In contrast, even the psalms present the reality of life's dangers (Psalm 3:1–2; 73:2–3).

Satan attempted to twist these very words when tempting Christ (Matthew 4:5–6). His implication was that the words written here could be applied as a demand to God: that Jesus could jump off a building and God would be obliged to keep Him from harm. Jesus rejected that interpretation (Matthew 4:7), in part by pointing out other important parts of God's Word (Deuteronomy 6:16).

Though Jesus rejected the Devil's improper use of these words, they do have some messianic implications. Often, during His earthly ministry, enemies tried to kill Jesus but could not, because it was not time for Him to die (John 7:30; 10:39). When the time came, He voluntarily laid down His life on the cross for our sins (Romans 5:8; 1 Corinthians 15:3; Galatians 1:4), though He could have summoned thousands of angels to rescue Him (Matthew 26:53).

Angelic servants are one of the ways in which God acts in the world (Genesis 19:1, 13; 2 Kings 19:35). Hebrews 1:14 teaches that angels are "ministering spirits sent out to serve for the sake of those who are to inherit salvation." No doubt, believers are not fully aware of the ministry of angels on their behalf, but it's possible that God allows them to intervene on our behalf.