Both Hagar and Mount Sinai were symbols of Jerusalem. They represented Judaism during Paul's time. Judaism continued to trust in the law and in being Abraham's descendants for their status before God (see John 8:31–59). They rejected Jesus as Messiah and remained bound to the law (Galatians 3:23–24; 4:1–3).
Mount Sinai in Arabia: Traditionally, Mount Sinai is located in the Sinai Peninsula in Egypt. However, some suggest that in Arabia means Mount Sinai was in Midian, where Moses once lived (see Exodus 3:1).