What does Exodus 4:23 mean?
God will command Egypt's ruler, through the words of Moses (Exodus 3:10), to release the nation of Israel from their enslavement (Exodus 1:13–14, 22). The Lord will explain the importance of Israel by comparing them to a first-born son. For much of human history, the oldest son has been a family's primary heir; they frequently receive the largest inheritance and the most resources. They are also expected to carry on the family name and legacy. When Pharaoh refuses to release Israel, it will be like holding a man's son hostage (Exodus 4:22).When Moses confronts Pharaoh it will begin a series of escalating plagues (Exodus 3:20). The climax of these disasters will be the death of Egypt's firstborn sons (Exodus 12:29–30). After all that Egypt experiences, this will be enough to convince Egypt's king to release the Hebrews (Exodus 12:31–32). Even that will only last so long (Exodus 14:8).
The prediction is also given here, it seems, to give context to a strange incident involving Moses, circumcision, and his son (Exodus 4:24–26). Moses escapes death when his wife Zipporah circumcises one of the two sons—either Gershom (Exodus 2:22) or Eliezer (Exodus 18:4). This act reconnects the family of Moses with the covenant of Abraham through circumcision, an important covenant practice (Genesis 17:9–10), prior to reuniting Moses with his own family (Exodus 4:27–28).