'Mount Sinai' in the Bible

This set of circumstances contains an illustration; for these two women [Hagar and Sarah] represent the two Agreements [between God and mankind]. The one [Agreement], given at Mount Sinai, represents Hagar, whose children became [the Israelites], enslaved under bondage [to the requirements of the law of Moses].

Now this woman, Hagar, is similar to Mount Sinai, in Arabia, and represents the present [earthly] Jerusalem [i.e., Israel], consisting of children in bondage [to the law of Moses].