The author of this psalm, and the occasion on which it was composed, are alike unknown. The psalm has no title; and there are no internal marks by which we can ascertain when, or by whom, it was written. It is very general in its application, and may have been composed with no particular reference to any event occurring at the time, as it is evident that it had no special reference to the circumstances of the writer. Though it follows a psalm composed by Moses, yet there is no reason to suppose that it was written by him, nor is there any particular resemblance to that psalm.
From some things in the psalm, as Psalm 91:3-5, Psalm 91:9,Psalm 91:11; it would appear to be not improbable that the psalm was composed with reference to some individual who was exposed to temptation, or to danger, either from secret enemies or from pestilence, and that it was intended to assure such an one that there was nothing to be feared if he put his trust in God. There is no evidence that it was designed to refer particularly to the Saviour. It is, indeed, applied to him by Satan in the temptation in the wilderness Matthew 4:6; but there is, in that case, no such recognition of its applicability to himself on the part of the Saviour as to justify us in the conclusion that it originally referred to him. Its quotation by the tempter is no proof that this was the original reference of the psalm, and the quotation made is one which could be applied to him in the same way as amy general premise in the Old Testament made to those who trusted in God might have been.
The most remarkable thing in the structure of the psalm is the frequent change of persons, leading some to suppose that it may have been composed with a view to its being sung by choirs in alternate responses, and Michaelis has suggested that there were probably two such choirs; the one - as in Psalm 91:1-2 - celebrating the praises of those who trusted in God; the other - as in Psalm 91:3-8 - exciting and encouraging the people to put their trust in God, and suggesting reasons why they should do it. Such a thing is, undoubtedly, possible; but the evidence that this was the intention of the author of the psalm is not clear.
Tholuck has divided the psalm, on the supposition that it was thus intended to be sung by alternate choirs, into portions arranged with that view: Psalm 91:1, the choir; Psalm 91:2, the response; Psalm 91:3-8, the choir; Psalm 91:9, the response; Psalm 91:10-13, the choir; Psalm 91:14-16, the response. This, however, is quite arbitrary, as it cannot be demonstrated to have been the original design.
This arrangement, however, suggests a good division of the psalm:
I. The general statement of the safety of those who put their trust in God, Psalm 91:1.
II. A responsive declaration of the author of the psalm, that he would make the Lord his refuge, and the Most High his habitation, Psalm 91:2.
III. A statement of the security or benefit of doing this, Psalm 91:3-8.
IV. A responsive declaration - repeated - by the author of the psalm that he would do this; that God "was" his refuge, Psalm 91:9 (part first).
V. A further statement of the benefit of this, Psalm 91:10-13.
VI. A general declaration embracing the sum of all that is said in the psalm, as coming from God himself, containing assurances of his protection to those who thus put their trust in him, and confide in him, Psalm 91:14-16.
This mode of division meets substantially all the changes of "persons" in the psalm, or arranges the different portions of it into parts belonging to the different speakers in the psalm. There is reason to believe that this was the line of thought in the mind of the psalmist, though it is not clear that this was designed to be so used in public responses in singing.

The safety of the godly man, and his confidence, Psalm 91:1, Psalm 91:2. How he is defended and preserved, Psalm 91:3-10. The angels of God are his servants, Psalm 91:11, Psalm 91:12; and he shall tread on the necks of his adversaries, Psalm 91:13. What God says of, and promises to, such a person, Psalm 91:14-16.
This Psalm has no title in the Hebrew; nor can it be determined on what occasion or by whom it was composed. It is most likely by the author of the preceding; and is written as a part of it, by fifteen of Kennicott's and De Rossi's MSS., commencing before the repetition of the four last words of the ninetieth. It is allowed to be one of the finest Psalm in the whole collection. Of it Simon de Muis has said: "It is one of the most excellent works of this kind which has ever appeared. It is impossible to imagine any thing more solid, more beautiful, more profound, or more ornamented. Could the Latin or any modern languages express thoroughly all the beauties and elegancies as well of the words as of the sentences, it would not be difficult to persuade the reader that we have no poem, either in Greek or Latin, comparable to this Hebrew ode."

INTRODUCTION TO PSALM 91
Jarchi and others think this psalm was written by Moses (m), as was the preceding; but the Targum ascribes it to David; as do the Septuagint, Vulgate Latin, Syriac, Arabic, and Ethiopic versions; and very probably, as is generally thought, was penned by him on occasion of the pestilence which came upon the people, through his numbering of them, 2-Samuel 24:1. The person all along spoken of, and to, according to the Targum, is Solomon his son; and, according to the title in the Syriac version, King Hezekiah, so Theodoret, who is called the son of David; neither of which are probable. Some think the Messiah is meant; and that the psalm contains promises of protection and safety to him, as man, from diseases, beasts of prey, evil spirits, and wicked men, under the care of angels; and this not because that Satan has applied one of these promises to him, Matthew 4:6, but because they seem better to agree with him than with any other: and one part of the title of the psalm, in the Syriac version, runs thus,
"and spiritually it is called the victory of the Messiah, and of everyone that is perfected by him.''
It seems best to understand it of every godly man, who is always safe under the divine protection. The Talmudisis (n) call it , "a song of the occursions", or "meetings with evil spirits.".

(Psalm 91:1-8) The safety of those who have God for their refuge.
(Psalm 91:9-16) Their favour with Him.

Talismanic Song in Time of War and Pestilence
The primeval song is followed by an anonymous song (inscribed by the lxx without any warrant τῷ Δαυίδ), the time of whose composition cannot be determined; and it is only placed in this order because the last verse accords with the last verse but one of Ps 90. There the revelation of Jahve's work is prayed for, and here Jahve promises: I will grant him to see My salvation; the "work of Jahve" is His realized "salvation." The two Psalm also have other points of contact, e.g., in the מעון referred to God (vid., Symbolae, p. 60).
In this Psalm, the Invocavit Psalm of the church, which praises the protecting and rescuing grace which he who believingly takes refuge in God experiences in all times of danger and distress,
(Note: Hence in J. Shabbath 8, col. 2, and Midrash Shocher tob on Psalm 91:1 and elsewhere, it is called, together with Psalm 3:1-8, (פגעים) שיר פגועין, a song of occurrences, i.e., a protective (or talismanic) song in times of dangers that may befall one, just as Sebald Heyden's Psalm-song, "He who is in the protection of the Most High and resigns himself to God," is inscribed "Preservative against the pestilence.")
the relation of Psalm 91:2 to Psalm 91:1 meets us at the very beginning as a perplexing riddle. If we take Psalm 91:1 as a clause complete in itself, then it is tautological. If we take אמר in Psalm 91:2 as a participle (Jerome, dicens) instead of אמר, ending with Pathach because a construct from (cf. Psalm 94:9; Psalm 136:6), then the participial subject would have a participial predicate: "He who sitteth is saying," which is inelegant and also improbable, since אמר in other instances is always the 1st pers. fut. If we take אמר as 1st pers. fut. and Psalm 91:1 as an apposition of the subject expressed in advance: as such an one who sitteth.... I say, then we stumble against יתלונן; this transition of the participle to the finite verb, especially without the copula (וּבצל), is confusing. If, however, we go on and read further into the Psalm, we find that the same difficulty as to the change of person recurs several times later on, just as in the opening. Olshausen, Hupfeld, and Hitzig get rid of this difficulty by all sorts of conjectures. But a reason for this abrupt change of the person is that dramatic arrangement recognised even in the Targum, although awkwardly indicated, which, however, as first of all clearly discerned by J. D. Michaelis and Maurer. There are, to wit, two voices that speak (as in Psalm 121:1-8), and at last the voice of Jahve comes in as a third. His closing utterance, rich in promise, forms, perhaps not unaccidentally, a seven-line strophe. Whether the Psalm came also to be executed in liturgical use thus with several voices, perhaps by three choirs, we cannot tell; but the poet certainly laid it out dramatically, as the translation represents it. In spite of the many echoes of earlier models, it is one of the freshest and most beautiful Psalm, resembling the second part of Isaiah in its light-winged, richly coloured, and transparent diction.