And all the children of Israel came to him: and he gave them in commandment all that he had heard of the Lord in mount Sinai.

Now this may be interpreted allegorically : these women are two covenants. One is from Mount Sinai, bearing children for slavery; she is Hagar.

I thought God gave the law,the Torah,on Sinai.

If he's equated the slave woman Hagar with Mt.Sinai,with Jerusalem in Judea, it seems like he's equating Hagar with the Jews, at least the law observant Jews,and he says,drive them out?

Do not return to Mt. Sinai.