“For a thousand years in thy sight are but as yesterday when it is past, and as a watch in the night” (Psalms 90:4).
Psalms 90, verse four, cited above, is famously the source for the concept so widely embraced among Bible Students, that a day with God is as a thousand years. The “day” we look forward to so much is the thousand year millennium of Revelation 20:1-6, in which Satan is restrained in the symbolic abyss, and the influence of sin which came from his deception of our first parents is gradually, but thoroughly, erased from mankind.
This psalm has an introductory superscription which says, “A prayer of Moses the man of God.” This seems odd, because verse 10 says the normal lifespan of man was about 70 years  — true enough for the time of David (who in fact lived 70 years),  whereas Moses lived to 120, Aaron to 123, and their elder sister Miriam presumably lived more years than either. Joshua lived to 110, and Caleb probably something on the same order. On the other hand, Numbers 26:62-65 tells us that most men of age 20 years and above about the time of the Exodus died in the wilderness before 40 years elapsed, so the lifespans limited to the 70 or 80 years mentioned in Psalms 90:10 were apparently common even in the days of Moses, by the end of the wilderness wandering.
“Before the mountains were brought forth or ever thou hadst formed the earth and the world, even from everlasting to everlasting, thou art God” (verse 2). This is a famous comment on the eternity of our creator. Even children reared in godly homes learn this statement, “from everlasting to everlasting,” and it puzzles the human mind with our limited sense of time. To imagine one continuing without end going forward is feasible. But to imagine one having no beginning backward in time runs counter to our entire experience, where everything temporal, physical, has a beginning — even the universe itself.
However, science may aid us a little in grappling with this counter-intuitive point. Since the days of Albert Einstein, we have learned that what seem to be stable quantities in the physical world — speed, size, mass, even time — are actually relative to the circumstances of the observer. Time passes more rapidly, or more slowly, to observers depending on relative velocities.  In fact, the very concept of time, a sequence of events in the physical world, is relative to the created universe that did not exist before it was initiated by the Creator in what was once derisively, but now popularly, termed the “big bang.” Thus, our sense of time is relative to the physical, the mundane, the created universe. This concept helps the mind a little in grasping that God is before, beyond, above, or external to this restraint — “from everlasting to everlasting, thou art God.”
The first part of verse two reminds us of Job 38:4, where Jehovah spoke to Job out of the whirlwind. “Where wast thou when I laid the foundations of the earth? declare, if thou hast understanding.” Some hold that Job was the same person called Jobab in Genesis 10:29, and this seems reasonable to us also. (Jobab was “of the east,” and Job was also “of the east,” compare Genesis 10:29, Job 1:3.) In this case Moses, studied in the wisdom of his time, would have known of that text in Job. Perhaps that text influenced Moses’ expression in Psalm 90:2.
Verses 3 to 10
Verses 3 to 10 are a brief overview of the experience of mankind from the curse to redemption. “Thou turnest man to destruction; and sayest, Return [to the earth], ye children of men ... thou carriest them away as with a flood; they are as a sleep ... in the morning [of our lives] it flourisheth, and groweth up; in the evening it is cut down, and withereth. For we are consumed by thine anger, and by thy wrath we are troubled. Thou hast set our iniquities before thee ... we spend our years as a tale that is told ... it is soon cut off, and we fly away.”
It is appropriate in this passage to give a time indicator in connection with the wrath of God, and hope for the future, as we have in verse four. “For a thousand years in thy sight are but as yesterday when it is past, and as a watch in the night.”
The key provided in this text is that a day is like a thousand years. The world has labored for 6000 years under sin and death. That would be six “days” according to the sense of this text. The world awaits the blessings of the Millennial “day” near at hand. Already, we are in a transition of the ages, apparent to those of faith. The world sees the commotion connected to this change, but does not perceive the meaning, and will not until the new day breaks. Then, after the introductory troubles, they will begin to hear the “still small voice” of peace calling out from Israel with their prophets restored (1 Kings 19:12, Zechariah 8:20-22).
In Israel it was customary to labor for six days and rest on the Sabbath. That day was set aside from mundane labor, both in order to focus on spiritual values and worship, and for rest and refreshment of the physical frame from the burdens of daily life. “Six days shall work be done: but the seventh day is the sabbath of rest, an holy convocation; ye shall do no work therein: it is the sabbath of the LORD in all your dwellings” (Leviticus 23:3).
This is a picture of the experience of mankind laboring for six days, six millennia, under the burden of sin and death, but resting from these burdens on the seventh millennium, a day for holiness and worship of God. The prophet Ezekiel mentions the same concept in the lengthy nine-chapter prophecy about the Millennial Kingdom that closes his book. “Thus saith the Lord Jehovah; The gate of the inner court that looketh toward the east shall be shut the six working days; but on the sabbath it shall be opened” (Ezekiel 46:1). For six thousand years the world remains outside the gate of access to God. But during the Millennium they will come to Him with praise, worship, and for instruction.
God is Not Slack Concerning His Promise
The time of the Adamic penalty has been long. But the lengthy lessons of sin and disobedience will seem in retrospect to be but a brief time, as they appear to God, simply six “days” of difficulty. The Apostle Peter picks up this point in his second epistle, and uses it to explain what otherwise seems to be an inordinate delay in the plan of God. “Beloved, be not ignorant of this one thing, that one day is with the Lord as a thousand years, and a thousand years as one day. The Lord is not slack concerning his promise” (2 Peter 3:8,9).
A Watch in the Night
This symbolism, a thousand years as a day, is well known among brethren of faith in God’s Plan of the Ages. However, the second part of Psalms 90:4 supplements this with another symbol on which less attention has been given. This second metaphor teaches the same concept. A thousand year period in this case is likened to “a watch in the night.”
The night watches mentioned in the scriptures are four in number, running from sundown to sunrise, approximately from 6 pm to 6 am, making each watch about three hours long. 
The daylight hours, approximately from 6 am to 6 pm, are also divided into four periods. There are two parts of the morning, and two parts of the afternoon.  If the night watches represent thousand year periods, then on the same scale, the four parts of the day would also represent thousand year periods. Six periods from daybreak take us to “midnight,” which is the hour of crisis for the world, introducing the Millennial Kingdom (compare Exodus 12:29, Acts 27:27).
There is another level of application, in which the days of a week apply on a smaller scale, not to the 7000 years of God’s Plan for mankind, but to the seven parts of the Gospel Age. For example, Leviticus 8:33 tells us that the consecration of the priesthood lasted seven days. This represents the Gospel age, that is shown as seven stages of time in Revelation chapters two and three.
Another example of seven days representing the seven parts of the Gospel Age is the seven days of trumpets in Joshua’s conquest of Jericho, representing the seven trumpet periods of Revelation (Joshua 6:12-16, Revelation 8:2).
The seven periods of the Gospel Age are also represented in the four daylight, and three succeeding nighttime, divisions of the Jewish day. In this respect, beginning at daybreak, the six periods leading to “midnight” take us through six periods of the Church. That introduces period seven, Laodicea (Revelation 3:14), the harvest of the Gospel Age (Revelation 3:20, Luke 12:36).
Thus, in pictures that refer to the Church, “midnight” marks the beginning of the Harvest. An example is Matthew 25:6, “at midnight there was a cry made, Behold, the bridegroom.” Another example is Psalms 119:62, “at midnight I will rise to give thanks unto thee because of thy righteous judgments.” On this level, the close of the harvest is the end of watch three, and the approach of watch four. This harmonizes with Matthew 14:25, where at the approach of “the fourth watch of the night, Jesus went unto them, walking on the sea,” a picture of Jesus receiving the saints at the close of the harvest, and quelling the raging storm of trouble. 
Verse 10 speaks metaphorically of the death of people under the curse: “it [our life] is soon cut off, and we fly away.” Of course people do not fly away anywhere. This is merely a poetic way of expressing the thought that people are no longer here among the living when they die. Psalm 146:4 tells us what happens at death. “His breath goeth forth, he returneth to his earth; in that very day his thoughts perish.”
Returning to earth refers to the fact that our bodies are buried and decompose back to the elements of the earth from which they are drawn. People do not “fly” to the grave in any real sense. They sleep in death, devoid of any sensation, until their time for resurrection during the Millennium comes. Until then, “there is no work, nor device, nor knowledge, nor wisdom, in the grave, whither thou goest” (Ecclesiastes 9:10).
Not all of the dead are literally buried in the earth. The circumstances are as varied in death as they are in life. Some are burned, some committed to the sea, some devoured by beasts or left to decay on a battlefield. What happens to the old body makes no difference to the prospect of resurrection.
For the consecrated people of God during the Christian age, their hopes are higher and more wonderful in every way than even the good prospects for the world. The saints of God are raised as heavenly beings with spirit bodies, in no way material or physical, but higher than anything earthly. That is the remarkable blessing God holds out to those who commit themselves to God during the present time, and live a life of faith.
Because Christ has already returned and we are already in the Harvest or ending period of the Gospel Age, that resurrection has already begun. The saints who died in centuries past have been raised. The process continues as the remaining members of the Church die here, until the Church is complete in glory by the end of the Harvest, and thereafter, until the last member of the Great Company class goes home as well.
Verse 11 refers to the power of God’s wrath. The penalty of death reaches wherever men are on the face of the globe. None escape its reaches. Some will live into the Millennial Kingdom and begin to be recovered from the curse and its effects before descending into the grave (Zechariah 14:16, Job 33:25). But until that time comes, the process continues unabated.
Meanwhile, those who have a heart for godliness are advised to use their time wisely in good ways. “So teach us to number our days, that we may apply our hearts unto wisdom” (verse 12). Numbering our days suggests that our time here is limited. We should avoid distractions that turn our attention away from our goal, which is Godliness in heart and mind.
Godliness does not come naturally. We must resist the natural tide of life, and apply our minds, our thoughts, and our time, toward spiritual things. Being responsible in working for our needs and for our dependents is part of the noble struggle of life that develops character. Being sidetracked with non-necessary secular pursuits is not.
Verses 13 to 17 close with a refrain of anticipation for the end of the present time of difficulty, and a sense of longing for the better things to come. For those who are consecrated to God now, this will be beyond the vail in the courts of glory. For the world of mankind, this will be when the blessings of the Millennium come to them.
“Return, O Jehovah, how long? and let it repent thee concerning thy servants [now under the burdens of the circumstances common to the world] ... O satisfy us early with thy mercy; that we may rejoice and be glad all our days [which will be everlasting]. Make us glad according to the days wherein thou hast afflicted us ... Let thy work appear unto thy servants ... And let the beauty of Jehovah our God be upon us.”
(1) It is interesting that seventy years is assigned to a normal lifespan here, because that is the residue remaining from 1000, after a life of 930 years. Adam lived 930 years, seventy years shy of the 1000 year limit that no one on record reached.
(2) There were remarkable exceptions even later. Jehoiada, the faithful priest and mentor of King Joash of Judah, lived to be 130 years old (2 Chronicles 24:15).
(3) These are not mere figments or simply mathematical constructs. The effects are real. Particles whose decay rate is constant, when accelerated to near the speed of light, decay more slowly from our frame of reference than those that are not thus accelerated.
(4) Mark 13:35 appears to refer to these four watches, “at even, or at midnight, or at the cockcrowing, or in the morning.” The morning watch would be the one just preceding morning.
(5) See Zion’s Watchtower Reprints, page 2953 (February 1, 1902).
(6) The King James version of Matthew 14:25 says “in the fourth watch.” But the Greek is tetarte, “to fourth” (Kingdom Interlinear, and Concordant Greek Text). That is, to-wards the fourth watch, as the fourth watch approached.