Galatians 4:25

25 Hagar is like a picture of Mount Sinai in Arabia. Also, she is like the city of Jerusalem here on earth now, because that city and its people are slaves under the authority of God's Law.

4:24 Mount Sinai was the place where God gave his Law to Israel's people. God's covenant with his people at that time was that they must obey the rules in his Law. So Israel's people were like slaves under the authority of God's Law.
4:25Arabia was a region south-east of Israel.