Why Are There Seven Days In a Week?

A strong case can be made that the origin of the seven-day week is God’s revelation of it in Genesis 2:1-3.

The Seven-Day Week Is Not Natural

It is significant to note that Genesis 2:1-3 explains the origin of the seven-day week. The seven-day week is unique from other cycles in that it is not natural in origin.

1. A year is determined from the solar cycle of solstices and equinoxes.
2. Seasons are also determined from the cycle above.
3. For the Hebrews, months were determined from the cycles of the moon. A new moon would signify a new month.
4. Days are determined by the cycle of daylight and darkness.

In contrast, the seven-day week is not determined from any natural cycle. Thus, William Dana writes this:

the creator of the week, in creating a cycle so out of harmony with nature, must havea had in view an important end. That conclusion follows from the abnormal character of the period; unless it performed a high service, no excuse for the existence of the intruder could be found.

William B. Dana, A Day for Rest and Worship: Its origin, Development and Present Day Meaning (Fleming H. Revell, 1911), 62.

The Seven-Day Week Is Not Based on Moon Phases

John McClintock and James Strong write, concerning the word “week”:

the week is a most natural and nearly an exact quadripartition of the month, so that the quarters of the moon may easily have suggested it.

McClintock, John and James Strong, Cyclopedia of Biblical, Theological, and Ecclesiastical Literature, Supplemental Volume, S.v..

Harold Dressler writes:

[The seven-day week] reflects a simple, observational calculation based on the moon-phases.

Dressler, Harold From Sabbath to Lord’s Day, 37, fn. 31.

However, when we examine the phases of the moon, we see that it is very unlikely that they are the origin of the seven-day week. Robert Martin writes this:

The facts, however, weigh against the idea of a lunar connection. Neither the phenomenon in question nor the calculation are siomple. The moon phase (synodic) cycle is 29.53 days, while the sidereal month (calculated with reference to fixed stars) is 27.32 days. The calendrical month, calculated at 1/12 of the solar year is 30.42 days. This timing of the moon’s phases, therefore, shifts by an average of about one day for each successive month, so that the lunar year (354 days) differs markedly from the solar year (365 days). Further, the new moon, which figures so prominently in Israel’s calendar, does not occur every 28 days. In a word, the seven-day week may not be traced to any natural cycle.

Martin, Robert Paul, The Christian Sabbath: Its Redemptive-Historical Foundation, Present Obligation, and Practical Observance (Trinity Pulpit Press, 2016), 41.

Pagan Influences Upon the Seven-Day Week

The seven-day week that we have today is a combination of biblical and pagan ideas. For example, in the planetary week, the days are named after planets and Nordic deities (e.g., Saturn’s-day, Sun’s-day, Moon’s-day, Wodan’s-day, Thor’s-day). However, Willy Rordoft writes this:

If we study its origins, we shall not be able to rid ourselves of the suspicion that the planetary week originated after the Jewish week and that it has impregnated the Jewish week with astrological ideas.

Willy Rordorf, Sunday: The History of the Day of Rest and Worship in the Early Centuries of the Christian Church, trans. A. A. K. Graham (Philadelphia: The Westminster Press, 1968), 9.