'Two' in the Bible

Now the mediator or go-between [in a transaction] is not [needed] for just one party; whereas God is only one [and was the only One giving the promise to Abraham, but the Law was a contract between two, God and Israel; its validity depended on both].

For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.

Which things are an allegory: for these are the two covenants; the one from the mount Sinai, which gendereth to bondage, which is Agar.