In Gadbois' post he argues that the Federal Vision "seems to have to marginalize adult baptisms, because it doesn’t fit nicely into what they view as the 'norm' for baptismal efficacy. Various manifestations of the doctrine of baptismal regeneration (and, yes, I realize there is no uniform definition of this doctrine) seem to depend on making infant baptisms paradigmatic." Gradbois says this is because when a adult is baptized it is done after a profession of faith. Thus, the adult being baptized is already justified before baptism (assuming his faith is God given, saving faith). This shows, as Gradbois argues, that the adult baptism does not effect his justification.
This argument seems straightforward and difficult for the Federal Vision position. Pastor Wilson sets out to defend the Federal Vision from this charge by quoting the Westminster Standards:
The efficacy of Baptism is not tied to that moment of time wherein it is administered; yet, notwithstanding, by the right use of this ordinance, the grace promised is not only offered, but really exhibited, and conferred, by the Holy Ghost, to such (whether of age or infants) as that grace belongs unto, according to the counsel of God's own will, in His appointed time (28.6).Wilson argues that baptism can work even before it is applied. That is, the act of saving faith done on the part of the adult is done because they will in the future be baptized. God is working in the adult in light of what will happen in the future.
All who hold to the Westminster will gladly agree that an infant's baptism can work after the baptism. This is clear in the section of the Confession quoted. But working backwards? This response of Wilson's is clever, I must admit that, but it seems to be lacking exegetical warrant. I am unaware of any passage that speaks of baptism working retroactively. More exegetical work needs to be done before this should be seen as a valid response. Further, is there any evidence that the Westminster Divines saw baptism working retroactively? If not, why are we to read this section of the Confession that way?
This response seems to be grasping for straws. It would appear that this is just another problem with the FV position. I am not sure how many "wholes" need to be shown in this view before it is abandoned, but one more cannot hurt.