Why did God send Hagar back to Abraham and Sarah before the child was born?
God sent Hagar back to Abraham and Sarah before the child was born so that she would go through the same experience thirteen years later, and so that a New Testament lesson could be provided. The purpose was not merely Hagar's immediate situation, but to prepare a lesson for future New Testament understanding.
Les explains that God sent Hagar back to the tent of Abraham and Sarah even before the child was born, just so she would have to go through the same thing thirteen years later. The reason given is so that we could have a New Testament lesson. He connects this to Peter's situation in Acts 15: after twelve years, God providentially and sovereignly reminds Peter of what happened in the house of Cornelius, preparing him to come to Paul's defense. Though God wanted Cornelius' house saved, the bigger picture was preparing Peter for that Acts 15 event.