Michael LeFebvre (The Liturgy of Creation) argues that the Pentateuch is a text for worshipers, not for historians. The difference is significant. A modern historian is charged with uncovering facts, who, what, when, where, how, and why. A worshiper is concerned with only a few of these - specifically why and who as they pertain to worship. Precise dates, so important to our modern mind, were not all that important to the ancient author and audience. Dates, when given, have more symbolic than historical significance.
There are only a handful of dates events in the Pentateuch - connected with the exodus or with the story of Noah. In chapter 4 of The Liturgy of Creation Lefebvre runs through all of these. The dates are connected to the major festivals of Israel and serve to anchor these to both events in the story of Israel and to the agricultural year.
Dates link a historical memory to the specific festivals that later Israel observed. The dates of the festivals are set by the heavenly lights and naturally occurring seasons and harvests of Canaan (as we saw in chapters one through three). The timing of the festivals are not based on the historical events they commemorate. Rather, the reverse is the case. The historical events are ascribed with the dates of Israel's festivals in order to associate those memories with later Israel's progress through each year's calendar. (p. 60)
This is not a concept we should find entirely foreign. We do something similar as Christians when we celebrate the birth of Jesus near the winter solstice in the Northern Hemisphere. But it teaches us how to read and consider the dates given in the Genesis (connected with the flood) and in the exodus story.
After running through the dates assigned to events attached to the major festivals LeFebvre turns to the new moon days. This provides an interesting example. Miriam, Aaron, and Moses all died on new moon days. Miriam died on the first new moon day (New Year's day) of the fortieth year following the exodus from Egypt (Num. 20). Aaron died on the first day (new moon day) of the fifth month of the same year (Num. 33:38). Moses died six months later on the first day (new moon day) of the 11th month of the same year (Deuteronomy 1:3; 32:48). The old generation had passed away and the people were prepared to enter the land of promise under Joshua, the new leader. LeFebvre suggests that "all three prophet siblings are identified with new moon day memorials spread through the year as settings to remember their faithfulness and examples to mothers, priests, and fathers of Israel." (p. 73) Although it is certainly possible that all three happened to be taken on the first day of spaced out months in the fortieth year, it seems more likely that there is a symbolic and liturgical significance to these dates. The same is true of the other dated events in the text.
Both the Noah story and the exodus story - the only stories in the Pentateuch tied to dates in Israel's calendar - are also tied to God's provision of sanctuary for his people. "Dates serve to link those two "temple inauguration" histories to the annual worship festivals of later Israel." (p. 77)
[T]he Pentateuch's narratives are designed as texts for worshipers (not strictly historians). Israel's calendar was "read" in the skies, "told" in their calendar narratives, and practiced in their patterns of labor and worship. Through the festival calendar and festival-dated narratives, Israel was taught to identify with the faith lessons of their heritage in cadence with the agricultural seasons of the land. Worship provided guidance for stewardship of the land in faithfulness and fruitfulness. (p. 77)
The specific dates in the calendar assigned to events in both the flood narrative and in the exodus narrative serve a symbolic and liturgical purpose. They do not exist to provide a journalistic account of events for modern (or ancient) historians.
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