Although it is not entirely unique in the Psalter, the most striking thing about Psalm 91 is that it ends with a divine speech in verses 14-16.
Usually when God speaks in the Psalms, it is to express divine displeasure and to call people to account. See, for instance, Psalms 50:7-23; 81:6-16; and 95:8-11, although it is interesting that 50:15, 23 and 81:16 suggest that God "will deliver," "will show . . . salvation," and "would satisfy," if the people will listen and respond faithfully. It is perhaps not coincidental that the very things that Psalms 50:15, 23 and 81:16 anticipate are what God explicitly promises in 91:14-16 (the Hebrew verb translated "deliver" in 50:15 is rendered as "rescued" in 91:15).
Indeed, the exact verbal links among these three psalms that contain divine address -- Psalms 50, 81, and 91 -- are striking enough to suggest that Psalms 50 and 81 intentionally anticipate Psalm 91; or perhaps more precisely, they anticipate Psalms 90-91 at the beginning of Book IV of the Psalter.
Psalm 89 at the end of Book III has articulated the crisis of exile by relating the failure of the Davidic covenant (see verses 38-51). In what seems to be an intentional response, Book IV begins with a prayer attributed to Moses, as if Moses were interceding for the people in exile as he did for the wilderness generation when the covenant was in jeopardy (see Exodus 32:1-14, and see the commentary on Psalm 90:12-17, Twentieth Sunday after Pentecost).
Following upon Psalm 90, Psalm 91:14-16 seems to suggest that the prayer of Moses has been answered. Verse 16a -- "With long life I will satisfy them" -- is an especially appropriate response to the petition of 90:14, repeating the verb "satisfy" and offering "long life" to people who in Psalm 90 were acutely aware of human transience. In response to Moses' intercession, God promises to do the things that Psalms 50 and 81 have said that God had been wanting to do all along, but that God apparently was unable to effect among an inattentive and uncooperative people.
The contrast between the divine address in 90:14-16 and the earlier divine speech in Psalms 50 and 81 suggests that the people's response to God is crucial, in terms of whether or not they experience the deliverance, salvation, and satisfaction that God wills for them. This does not mean that God will deliver the people only when they obey and thus deserve God's favor.
Rather, it suggests that the favor God always offers will be ineffective among an unreceptive, untrusting people. Thus, it is crucial that the divine promises in Psalm 91:14-16 are preceded in verses 1-13 by an eloquent profession of trust. Again, it is as if the prayer of Moses in Psalm 90 has been answered -- that is, the people have been able to "gain a wise heart" (90:12), which means they have renounced autonomy and thus have fully entrusted themselves and their future to God. Indeed, it is precisely such trust that constitutes deliverance, salvation, and satisfaction (see Psalm 9:9-10).
To be sure, readers and interpreters of Psalm 91 have not always understood this. Rather, the promises expressed in verses 1-13 and reinforced by the divine address in verses 14-16 have often been understood as something like a magical guarantee against any form of opposition or distress. Granted, several of the promises seem to point in this direction, including verses 9-13 that begin the lection for the day; however, we are dealing here with poetic hyperbole.
The keyword in Psalm 91 is "refuge" (see verses 2, 4, 9; see also 2:12; 5:11; 7:1; 11:1; 16:1, and often in the prayers for help), which assumes the need for protection and help. And the protection and help that God promises assumes the existence of all manner of trouble and opposition, especially in verses 3-13 -- enemies, illness, and ferocious attack by people and animals (although the animals in verse 13 may be metaphors for human opponents).
As for verses 14-16, it is to be noted that the divine promises are stated primarily by seven finite verbs. Since the number seven often symbolizes fullness or completion, this is probably not coincidental -- that is, God promises complete assurance. But there is an eighth element in verses 14-16; and it stands out by virtue of being near the center of the sequence, as well as by being the one promise stated in a verbless clause.
It is the middle element of verse 15; and a literal translation is as follows: "with him [am] I in trouble" (emphasis added). As the added emphasis indicates, the divine promise assumes the existence of trouble and opposition. In short, the deliverance, salvation, and satisfaction that God promises do not mean a care-free, unopposed life. Rather, those who fully entrust themselves to God experience deliverance, salvation, and satisfaction in the midst of opposition and trouble.
The context of the Psalter reinforces this conclusion. The righteous prayers of the psalmist are never without opposition or trouble (which, of course, is why the prayers for help are generally known as laments, complaints, or protests). Then too, this conclusion is reinforced by the way verses 11-12 show up in the New Testament.
In Matthew 4:5-7 and Luke 4:9-12, the devil cites verses 11-12 in an attempt to entice Jesus to throw himself down from the top of the Temple. While it is interesting to see that the devil knows the Psalms, his misappropriation of verses 11-12 is instructive. Jesus' refusal to embrace the devil's interpretation suggests that to claim the promises of verses 11-12 for self-serving purposes is unfaithful. It amounts to testing God rather than trusting God. Jesus will not claim the promises of Psalm 91 as a way to avoid suffering. Rather, when Jesus claims the promise of divine protection and help, it is from the cross (see Luke 23:46, quoting Psalm 31:5).
In conclusion, it should be noted that the promise at the heart of the divine address -- "with him [am] I in trouble" (verse 15) -- is the same promise that lies at the heart of another of the Psalter's most eloquent psalms of assurance/trust: "for you are with me" (Psalm 23:4).
This promise comes, of course, in the midst of "the darkest valley." As the psalmists knew, and as Jesus revealed as well, the delivering, saving, satisfying presence of God does not prevent trouble, opposition, and suffering. Rather, it promises the strength to persevere, endure, and overcome (see Romans 8:31-39).