A Quick but Important Note on Adamic Imputation
Turretin on imputation: "The question does not concern all his posterity who in any way were to spring from him, but only those who descend from him in the ordinary way of generation (so that Christ may be excluded, who not in the ordinary way, but in an extraordinary and supernatural way, was conceived by the power of the Holy Ghost".
Baptist Catechism Question 19: The covenant being made with Adam, not only for himself but for his posterity, all mankind descending from him by ordinary generation sinned in him, and fell with him in his first transgression
These statements are not necessarily incorrect, but they can be misunderstood in an incorrect way apart from qualification that I don't believe is offered as often as it should be.
The issue is that they may sound as if not being born by ordinary generation is the cause/reason/basis of not being in the Adamic Covenant. The reality is the other way around: not being in the Adamic Covenant is the cause/reason/basis of not being born by ordinary generation. Rather, the statements must be understood as descriptive of those within the Adamic Covenant.
To see the reason for this, one simply must ask the question why it is that Christ was not in the Adamic Covenant (which is the only reason the qualification "by ordinary generation" is added anyways). The answer is that Christ, "was not a human person and therefore not in the covenant of works" (Berkhof, Systematic Theology 243). Christ was a divine person and this existed before the Adamic Covenant was made. Since federal headship is immediate, so is imputation. Adam's sin is imputed immediately to persons, not to natures. Thus, when you add in the fact that sin nature is itself a judicial consequence of the prior imputation of Adam's sin (which can be seen in that even the creation of the soul destitute of original righteousness is itself an effect of the imputation of Adam's sin), it becomes obvious that the reason that Christ was born in a supernatural way was because he wasn't in the Adamic Covenant (thus the Holy Spirit had to shield his human nature from inheriting original inherent sin from Mary who had received such inherent sin from the imputation of Adam's sin to her own person)1 and not the other way around.
The important thing to keep in mind here is that while original sin is the consequence of imputation, it is also a defect that is passed on by means. This means that while Mary inherited inherited original sin because of the imputation of Adam's sin directly to her person, she still receives the defect of original sin by means of natural generation from her parents who also had such a defect.
Christ, on the other hand, did not have Adam's covenantal sin imputed to Him (obviously the act itself was imputed to Him in that He died for all of Adam's sins including this sin, but it was not imputed to Him as the sin of the Adamic Covenant) because He was not in the Adamic Covenant. Thus, the Holy Spirit conceiving Christ in a supernatural way is a matter of justice so that He would not receive a sin nature from Mary and thus bear the consequences/covenantal penalty for a sin that was not actually imputed for Him in a covenant that He was not actually in (see Bavinck Vol 3, 294).
1
Some actually deny that Luke 1:35 has any relation to keeping Jesus from receiving original sin, in which case, assuming also a non-physical transmission of sin (see my comments on van Mastricht below) my comments following this footnote are unnecessary. For example:
“That miraculous nativity from the virgin really bears no other relation to the holiness of the conception and nativity of Christ, but that of a symbol, appointed by God, whereby he was separated from sinners"
—Johann Cloppenburg, quoted in Witsius, Economy of the Covenants, vol. 1, p. 197.
This also relates to a paper I really want to write one day regarding Turretin and van Mastricht's conceptions of the propagation of sin. I will definitely have more to say then than I do now. Petrus van Mastricht would also seem forced to take the symbolic interpretation of Luke as I understand him (to be sure, he mentions the verse in relation to Christ being set apart and never contracting sin, but it isn't clear how exactly he understands this), because he seems to deny that corruption is transmitted physically, but that natural generation is obviously a prerequisite for "transmitting" corruption (in so far as a new soul/body is brought into the world) yet the corruption itself is solely a result of imputation by which original righteousness is withheld as punishment (Vol 3, pg. 455-456, 474-476). Turretin, on the other hand, allows for bodily transmission of corruption through an unclean seed (Vol 1, 636-643). At least this is my current reading of them. The question is whether concupiscence/inherent corruption/pollution/the disorder between soul and body is solely the result of the withholding of original righteousness or if there is a physical aspect involved. Van Mastricht’s solution taken together with the symbolic interpretation is much simpler, thus in this post, I tried to explain how the more complex solution of Turretin/Bavinck ought to be understood.