How did Abraham and Sarah have a child after waiting 36 years?
After 36 years of God's promise with nothing happening, Abraham and Sarah took matters into their own hands rather than waiting. They obtained a child through Sarah's Egyptian slave girl Hagar, not through Sarah herself. Sarah later became upset and sent Hagar away, but the Lord sent Hagar back.
Les teaches that God promised for 36 years that Abraham and Sarah would have a son, yet nothing happened. Finally, after those 36 years, they took matters into their own hands and had a child by virtue of the slave girl, the Egyptian Hagar. Sarah was so upset with Hagar's reaction that she sent her away, probably in almost a rage. While Hagar was out in the desert, the Lord appeared to her and said, “You go back to Sarah's tent.” Les emphasizes that God sent her back and wants us to ask why, since it was going to be the same thing all over again.