Because of the apostle’s testimony, Gal. iv. 24, “These are the two covenants; the one from Mount Sinai, which gendereth to bondage.” For the children of this Sinai covenant the apostle here treats of, are excluded from the eternal inheritance, as Ishmael was from Canaan , the type of it, ver. 30, “Cast out the bond-woman and her son; for the son of the bond-woman shall not be heir with the son of the free woman;” but this could never be said of the children of the covenant of grace under any dispensation, though both the law and the covenant from Sinai itself, and its children, were even before the coming of Christ under a sentence of exclusion, to be executed on them respectively in due time.
Paul contrasts Sinai to Abraham but where is the evidence that plugs this into the Covenant of Works? His argument assumes that all reference to “bondage” means a system of demanding perfect perpetual obedience as a condition of eternal life. But the Apostle Paul explains what he means by bondage and it is not what Boston presupposes:
I mean that the heir, as long as he is a child, is no different from a slave, though he is the owner of everything, but he is under guardians and managers until the date set by his father. In the same way we also, when we were children, were enslaved to the elementary principles of the world. But when the fullness of time had come, God sent forth his Son, born of woman, born under the law, to redeem those who were under the law, so that we might receive adoption as sons.
So, for Paul’s argument, the bondage is that of limitations due to immaturity. The point is that now that the new has come we must leave behind the old. Nothing is said about going all the way back to man’s state of innocence to where Adam, as a public person, was given a Covenant that demanded his perfect obedience to secure his own future and that of his posterity. It looks as if Boston has his own theological paradigm and really isn’t interested in the details contained in Paul’s own argument.
Boston offers other arguments, I’ll look at them later as I have time.