Many Biblical scholars claim that the data point to variant
versions of the different stories about Abraham. Thus, for
example, there are two accounts of his deceptions regarding Sarah,
one in 12:9-13:1, and the other in 20:1-17. The oldest version of
the story they believe is found in 26:1-14 and is told not of
Abraham but of Isaac, whose character it fits far more
consistently. Similarly there are three accounts of the covenant
with Abimelech (Gen. 21:22-31, 21:25-34, and 26:15-33). The two
accounts of the expulsion of Hagar and the birth of Ishmael, in
Genesis 16:1-16 and 21:1-20 differ rather widely in details. In
one account Hagar is expelled and Ishmael is born after the birth
of Isaac, and in the other before that event. Do these variant
versions indicate that they were drawn from different groups of
narratives? The differences in detail are in general closely
parallel to those which the New Testament student finds in the
different accounts of the same events or teachings in the life of
Jesus. They suggest to many that the author of the book of Genesis
was eager to preserve each and every story regarding Abraham.
Instead, however, of preserving intact the different groups of
stories, as in the case of the Gospels, they have been combined
with great skill. Sometimes, as in the case of the expulsion of
Hagar, the two versions are introduced at different points in the
life of the patriarch. More commonly the two or more versions are
closely interwoven, giving a composite narrative that closely
resembles Tatian's Diatessaron which was one continuous narrative
of the life and teachings of Jesus, based on quotations from each
of the four Gospels. Fortunately, if this theory is right, the
group of stories most fully quoted and therefore best preserved is
the early Judean prophetic narratives. When these are separated
from the later parallels they give a marvelously complete and
consistent portrait of Abraham.