It is important to understand that while Genesis appears to be a chronological telling of creation and events of Abraham’s people, deep study reveals that some events must be understood to have taken place at nearly the same time or prior to the events being described. For St. Augustine this was so important that he included this distinction in his Christian Instruction.
Augustine explains: “In the Scriptures some things are related in such a way that they seem to be following the order of time or occurring in chronological succession, when actually the narrative, without mentioning it, refers to previous events that had been left unmentioned. Unless we understand this distinction, we shall fall into error. For example, we find in Genesis: ‘And the Lord God planted a paradise of pleasure in the east; and there He put the man whom He had formed. And out of the ground the Lord God made to grow every tree that is pleasant to the sight and good for food.’ This last mentioned event would seem to have occurred after God had made the man and placed him in paradise. After both these facts have been mentioned briefly (that is, that God planted a paradise and there ‘placed man whom He had formed’), the narrative turns back by means of recapitulation and relates what had been planted and that God brought forth out of the ground all manner of trees fair to behold and pleasant to eat of.” (Christian Instruction 2:36.52)
Another example involves Abraham’s cousin wife, Keturah. The narrative of Abraham’s wives has Sarah’s death and burial before it speaks of Abraham’s marriage to Keturah. This creates the impression that Abraham married Keturah after Sarah died, but that is not the case. He married her shortly after he settled in the land of Canaan, his mother’s homeland. This second marriage enabled Abraham to gain territory in Canaan.
The narrative of Judah is another example. Judah is in Egypt to buy grain during the famine in Canaan. He was also in Canaan with his friends and there he has sexual intercourse with Tamar, the daughter of a priest. Judah was a worldly chief who traveled between Egypt and Canaan. Additionally, Genesis indicates that Judah had 2 wives, which means that he would have moved back and forth between their settlements.
Sometimes the arrangement of the Bible suggests a longer stretch of time than the actual genealogies permit. This is evident in the story of Oholibamah, the daughter Anah and grand daughter of Zibeon. Oholibamah was Esau’s wife (Genesis 36:5) who bore Korah, the Elder. Korah the Younger was a half-brother to Moses and resisted Moses' authority in the wilderness. He died when the earth opened and devoured him and his fellow conspirators (Numbers 26:10). This means that the events of Genesis 48-50 and the events described in the early chapters of Exodus must be understood as involving no more than 5 generations.
It is clear then that reading Genesis strictly as a chronological account leads to erroneous conclusions. The material is organized with a chronological sequence, but when we examine the genealogical material in Genesis we discover that some of the recounted events happened concurrently and some took place beforehand.