And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so. And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also. And God set them in the firmament of the heaven to give light upon the earth, And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good. And the evening and the morning were the fourth day.
The fourth day is at the center of the creation’s septenary. The importance of what is being created on this day is given by the fact that it is in a deep relationship with both the first and with the seventh day of creation. The fourth day is related to the first one because in the first day was created the light – in Hebrew ‘or – which doesn’t exactly coincide with the light emanating from the sun and the stars. Indeed the lights of the firmament are intended as simple lamps – in Hebrew ma’or – and not as the source of light. Moreover there is a certain technicality in the description of the sun and moon that are not named by name. In the Genesis’ account the sun and the moon don’t have divine attributes, because they are simple sources of light with specific functions.
The sun and the moon – i.e. the great lights – served primarily to separate day from night. For the last time is used the verb to separate – in Hebrew the hiphil of badal – that was repeated several times in the first four days of creation. But there is also another important verb, the hebrew mashal i.e. to rule. The sun and the moon are reference’s points for the cultic calendar. In the KJV (i.e. King James Version of the Bible) the hebrew word mo’ed has been translated as seasons. The term mo’ed should be more appropriately translated as religious festivals, because the priestly author of this chapter was very interested in cultic matters (cfr. also Num 10:10; Isaiah 33:20). In fact, the oldest and deepest meaning of the jewish festivals is tied to the succession of seasons (i.e. the main meaning of mo’ed). So the sun and the moon are signs – in Hebrew ‘ot – to scan the sacred time and not only the profane time.
Why then the fourth day’s creation is at the center of the creation’s week? Some scholars think that behind this there is the so-called calendar of Sabbaths. This calendar was known by the Book of Jubilees, a key text of Enoch tradition. It is a 364-day calendar made by four quarters of 30 days. To each quarter has to be add a day. So every quarter is made of thirteen weeks (i.e. 91 days = 30 × 3 + 1). This organization of the calendar permitted that the first and the 15th day of each month of the first quarter fell exactly on the fourth day of the week. And it was in this fourth day that fell the most important festivals in the Jewish calendar, i.e. the New Year’s, Easter and Feast of Tabernacles. In this way the main festivals of the jews never fell on a Saturday.
It is also believed that following the abandonment of this calendar, to conform it to the official lunar calendar used in the Hellenistic cultural contexts, some Jews turned away from Jerusalem and settled in Qumran.