As we read of Abraham we are drawn to parallels between:
(a) Abraham dealing with daily life while awaiting the full reality of a covenant fulfilled; and
(b) Us dealing with life, death, faith, fear, conflict, contracting, transacting, marriage, and family estrangement, while awaiting a transcendant reality of open, unending communication and friendship with God.
What, if anything, do we learn from Abraham and Sarah? What do we learn about God?
In the middle of the relatively mundane, Abraham is asked by God to sacrifice his "only son" as a burnt offering. There is much to ponder in this story alone. Clearly, Isaac was not his "only son" since we have just observed God covenanting with Hagar in the previous chapter -- "I will make Ishmael into a great nation". And, we know that God finds child sacrifice to be an abomination (Deut 12:30,31) and that he instructs "Thou shalt not kill".
The story is presented fairly straightforwardly as a test from God that Abraham actually passes. And most sermons and children's books on this story remain at this level of understanding. While this is clearly a correct understanding of the story (Heb 11:17-19), I would encourage you to grapple with this story a little this week and dare to think more expansively about it.
Advanced study: If you have time, look at the parallels between the life of Hagar and that of Moses. We have previously noted parallels between Moses and Christ, but the more you look in the Old Testament, the more you find themes that point our minds to Christ. Here's a place to start -- there is a lot of wandering in the wilderness/desert in the Bible, and Hagar does some wandering in Chapter 20.