This psalm is one of the most remarkable in the whole collection. It is said, in the title, to be "A Prayer of Moses, the man of God;" or, as it is in the margin, "being a Psalm of Moses." The original word - תפלה tephillâh - means properly
(1) intercession, supplication for anyone;
(2) prayer or supplication in general;
(3) a hymn or inspired song.
Gesenius, Lexicon. In Psalm 72:20, the word is applied to the whole preceding part of the Book of Psalm - "The prayers of David, the son of Jesse, are ended." The word "prayer" would better represent the nature of the contents of this psalm than the word "psalm," or "hymn."
If the author was Moses, then this is the only one of his compositions which we have in the Book of Psalm. We know, from not a few places in the Pentateuch, that Moses was a poet as well as a lawgiver and statesman; and it would not be improbable that there might have been some compositions of his of this nature which were not incorporated in the five books that he wrote, and which would be likely to be preserved by tradition. This psalm bears internal evidence that it may have been such a composition. There is no local allusion which would make it necessary to suppose that it was written at a later period; there is nothing inconsistent with the sentiments and style of Moses in the Pentateuch; there is much that is in accordance with his style and manner; and there were numerous occasions when the sentiments of the psalm would be exceedingly suitable to the circumstances in which he was, and to the train of thoughts which we may suppose to have passed through his mind. The following remarks of Prof. Alexander seem to me to be eminently just and appropriate: "The correctness of the title which ascribes the psalm to Moses is confirmed by its unique simplicity and grandeur; its appropriateness to his times and circumstances; its resemblance to the law in urging the connection between sin and death; its similarity of diction to the poetical portions of the Pentateuch, without the slightest trace of imitation or quotation; its marked unlikeness to the Psalm of David, and still more to those of later date; and finally the proved impossibility of plausibly assigning it to any other age or author." As a relic thus of most ancient times - as coming down from the most remarkable man in the Jewish history, if not in the world - as well as for its own instructive beauty and appropriateness to all times and lands - it is a composition of great interest and value.
This psalm is placed at the beginning of the fourth book of the Psalter, according to the ancient traditional division of the Psalm. Or, perhaps, the author of the arrangement - probably Ezra - designed to place this "by itself" between the two great divisions of the book, containing respectively the earlier and the later psalms. It may be regarded, therefore, as "the heart or center of the whole collection," suggesting thoughts appropriate to the entire current of thought in the book.
The phrase, "the man of God," in the title, is given to Moses in Deuteronomy 33:1; Joshua 14:6; Ezra 3:2; as a title especially appropriate to him, denoting that he was faithful to God; that he was a man approved by God. The title is indeed given to others, Judges 13:6, Judges 13:8; 1-Samuel 2:27; 1-Samuel 9:6-8; 1-Kings 12:22, et al.; but there was a special appropriateness in the title as given to Moses on account of his character, his eminent rank, and his influence in founding the Hebrew commonwealth.
It is impossible, of course, now to determine the time when the psalm was composed, but it may not improbably be supposed to have been near the close of the wanderings in the wilderness. The Hebrew people were about to enter the promised land; the generation that came out of Egypt was passing away; Moses himself felt that he was near the end of his course, for he had been apprized that he could not enter the land of promise to the borders of which he had conducted the people. These things were eminently suited to suggest such views of the shortness of human life, and of its frailty, as are here presented. At the same time, all these circumstances were suited to suggest the reference to the future, and the prayer in respect to that future, with which the psalm so beautifully closes. It seems, then, not improper to regard this psalm as one of the last utterances of Moses, when the wanderings of the Hebrew people were about to cease; when an entire generation had been swept off; and when his own labors were soon to close.
The main subject of the psalm is the brevity - the transitory nature - of human life; the reflections on which seem designed to lead the soul up to God, who does not die. The races of people are cut down like grass, but God remains the same from age to age. One generation finds him the same as the previous generation had found him - unchanged, and as worthy of confidence as ever. None of these changes can affect him, and there is in each age the comforting assurance that he will be found to be the refuge, the support, the "dwelling-place" of his people.
The psalm consists of the following parts:
I. The fact that God is unchanging; that he is the refuge of his people, and always has been; that from the eternity past to the eternity to come, he is the same - he alone is God, Psalm 90:1-2.
II. The frailty of man - the brevity of human life - as contrasted with this unchanging nature - this eternity - of God, Psalm 90:3-11. Man is turned to destruction; he is carried away as with a flood; his life is like a night's sleep; the human race is like grass which is green in the morning and is cut down at evening; - human existence is like a tale that is told - brief as a meditation - and narrowed down to threescore years and ten.
III. A prayer that the living might be able so to number their days - to take such an account of life as to apply the heart to wisdom; - to make the most of life, or to be truly wise, Psalm 90:12.
IV. A prayer for those who were to follow - for the coming generation - that God would continue his favors; that though the present generation must die, yet that God, who is unchanging and eternal, would meet the next generation, and all the generations to come, with the same mercies and blessings, enjoyed by those who went before them - prolonging these to all future time, Psalm 90:13-17.
The psalm, therefore, has a universal applicability. Its sentiments and its petitions are as appropriate now as they were in the time of Moses. The generations of people pass away as certainly and as rapidly now as they did then; but it is as true now as it was then, that God is unchanging, and that he is the "dwelling-place" - the home - of his people.

The eternity of God, Psalm 90:1, Psalm 90:2; the frailty of the state of man, Psalm 90:3-9; the general limits of human life, Psalm 90:10; the danger of displeasing God, Psalm 90:11; the necessity of considering the shortness of life, and of regaining the favor of the Almighty, Psalm 90:12; earnest prayer for the restoration of Israel, Psalm 90:13-17.
The title of this Psalm is, A Prayer of Moses the man of God. The Chaldee has, "A prayer which Moses the prophet of the Lord prayed when the people of Israel had sinned in the wilderness." All the Versions ascribe it to Moses; but that it could not be of Moses the lawgiver is evident from this consideration, that the age of man was not then seventy or eighty years, which is here stated to be its almost universal limit, for Joshua lived one hundred and ten years, and Moses himself one hundred and twenty; Miriam his sister, one hundred and thirty; Aaron his brother, one hundred and twenty-three; Caleb, four-score and five years; and their contemporaries lived in the same proportion. See the note on Psalm 90:4 (note). Therefore the Psalm cannot at all refer to such ancient times. If the title be at all authentic, it must refer to some other person of that name; and indeed איש אלהים ish Elohim, a man of God, a divinely inspired man, agrees to the times of the prophets, who were thus denominated. The Psalm was doubtless composed during or after the captivity; and most probably on their return, when they were engaged in rebuilding the temple; and this, as Dr. Kennicott conjectures, may be the work of their hands, which they pray God to bless and prosper.

INTRODUCTION TO PSALM 90
A Prayer of Moses the man of God. Here begins the fourth part of the book of Psalm, and with the most ancient psalm throughout the whole book, it being written by Moses; not by one of that name that lived in later times; nor by one of his posterity; nor by some one who composed it, agreeably to his words and doctrines, and called it by his name; but by that Moses by whom the Lord brought the children of Israel out of Egypt, led them through the wilderness to the borders of Canaan's land, and by whom he delivered to them the lively oracles; and who is described as the man of God, a title given to Moses, Deuteronomy 33:1, so called, not as a creature of his make, so all men are; nor as a man of grace, born of God, so is every saint; but a man of more than ordinary gifts received from the Lord, a prophet of the Lord, and the chief of the prophets, and a type of the great Prophet; so inspired men and prophets under the Old Testament bear this name, and ministers of the Gospel under the New, 1-Kings 17:18. It is a conceit of Bohlius, that this prayer of his (so it is called, as several other psalms are, see Psalm 17:1) was made by him when he was about seventy years of age, ten years before he was sent to Pharaoh, while he was in Midian, which he gathers from Psalm 90:10; others think it was written towards the end of his life, and when weary of it, and his travels in the wilderness; but it is more generally thought that it was penned about the time when the spies brought a bad report of the land, and the people fell a murmuring; which provoked the Lord, that he threatened them that they should spend their lives in misery in the wilderness, and their carcasses should fall there; and their lives were cut short, and reduced to threescore years and ten, or thereabout; only Moses, Joshua, and Caleb, lived to a greater age; and on occasion of this Moses wrote this psalm, setting forth the brevity and misery of human life; so the Targum,
"a prayer which Moses the prophet of the Lord prayed, when the people of the house of Israel sinned in the wilderness.''
Jarchi and some other Jewish writers (z) not only ascribe this psalm to Moses, but the ten following, being without a name; but it is certain that Psalm 95 was written by David, as appears from Hebrews 4:7 and Psalm 96 is his, compared with 1-Chronicles 16:23 and in Psalm 99 mention is made of Samuel, who lived long after the times of Moses.

(Psalm 90:1-6) The eternity of God, the frailty of man.
(Psalm 90:7-11) Submission to Divine chastisements.
(Psalm 90:12-17) Prayer for mercy and grace.

Taking Refuge in the loving-kindness of the Eternal One under the Wrathful Judgment of Death
The Fourth Book of the Psalm, corresponding to the ספר במדבר of the Pentateuch, begins with a Prayer of Moses the man of God, which comes out of the midst of the dying off of the older generation during the march through the wilderness. To the name, which could not be allowed to remain so bald, because next to Abraham he is the greatest man known to the Old Testament history of redemption, is added the title of honour אישׁ האלהים (as in Deuteronomy 33:1; Joshua 14:6), an ancient name of the prophets which expresses the close relationship of fellowship with God, just as "servant of Jahve" expresses the relationship of service, in accordance with the special office and in relation to the history of redemption, into which Jahve has taken the man and into which he himself has entered. There is scarcely any written memorial of antiquity which so brilliantly justifies the testimony of tradition concerning its origin as does this Psalm, which may have been preserved in some one or other of the older works, perhaps the "Book of Jashar" (Joshua 10:13; 2-Samuel 1:18), until the time of the final redaction of the Psalter. Not alone with respect to its contents, but also with reference to the form of its language, it is perfectly suitable to Moses. Even Hitzig can bring nothing of importance against this view, for the objection that the author in v. 1 glances back upon past generations, whilst Israel was only born in the time of Moses, is removed by the consideration that the existence of Israel reaches back into the patriarchal times; and there is as little truth in the assertion that the Piel שׂבּענוּ in Psalm 90:14 instead of the Hiphil brings the Psalm down into very late times, as in the idea that the Hiph. והאבדתּ in Psalm 143:12 instead of the Piel carries this Psalm 143:1-12 back into very early times. These trifling points dwindle down to nothing in comparison with the fact that Psalm 90 bears within itself distinct traces of the same origin as the song האזינו (Deut. 32), the blessing of Moses (Deut. 33), the discourses in Deuteronomy, and in general the directly Mosaic portions of the Pentateuch. The Book of the Covenant, together with the Decalogue (Exodus 19:1) and Deuteronomy (with the exception of its supplement), are regarded by us, on very good grounds, as the largest originally Mosaic constituent parts of the Pentateuch. The Book of Deuteronomy is תּורת משׁה in a pre-eminent sense.