[From your post on the Westminster Confession:] It also teaches that [in the sacrament of baptism] "the grace promised is not only offered, but really exhibited, and conferred, by the Holy Ghost" . (Chapter XXVIII.6)
I admit that this one is tricky. However, take a look at what it says one chapter earlier:
WCF - Chap. XXVII . 3 - III. The grace which is exhibited in or by the sacraments rightly used, is not conferred by any power in them; neither does the efficacy of a sacrament depend upon the piety or intention of him that does administer it: but upon the work of the Spirit, and the word of institution, which contains, together with a precept authorizing the use thereof, a promise of benefit to worthy receivers.
Now, let's quote your section fully:
WCF - Chap. XXVIII . 6 - VI. 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.
Therefore, when we put the two together we may conclude that the actual "act" of baptism confers no salvific grace at all, however, the Holy Spirit will confer grace at baptism as He so desires. Reformers do not believe that one minute before baptism a person is unsaved and one minute after he IS saved. Reformers believe that salvation is by grace alone, through faith (Eph. 2:8-9).
Why then do you baptize infants? (Or are you a Reformed Baptist?)
I am a Reformed Baptist who attends a Southern Baptist church. My understanding of why most Reformers baptize infants is that it is a Covenant Baptism. It is a sign and a seal, but it is NOT salvific.
-A8
If the Holy Spirit does not do anything in baptism, then there is no "efficacy of Baptism". And if grace is not conferred by the Holy Spirit in baptism, then the claim that "by the right use of this ordinance, the grace promised is not only offered, but really exhibited, and conferred, by the Holy Ghost" is simply false. They can't have it both ways. Either grace is conferred through the sacraments or not.
-A8