One of the most striking features, to my mind, of these stories is that many of the episodes in Avraham's life seem like repetitions, or at least the stories are intertwined. Let us examine the evidence:
ch.12 – Sarah taken by Pharaoh /Ch.20 Sarah taken by Avimelech
Ch.14 – Saving Lot / Ch.19 – Saving Lot
Ch.16 - Hagar runs away / Ch.21 – Hagar sent away
Ch.17 - Promise of Yitzchak's birth / Ch.18 - Promise of Yitzchak's birth
Ch.21 Avraham gives up his son / Ch.22 – Avraham gives up his son
Maybe we can add to this TWO stories of covenants (ch.15 and 17) and two Avimelech stories (ch.20 and 21) What does all this mean? Why do the stories of Avraham appear in "pairs"?