What is baptism about, more theologically?

From some correspondence with a friend...

I like the joint FV statement on baptism and justification, and don't think it conflicts with Westminster Confession 28:6, which is quite striking in its language about what baptism does... for the faithful. That's the rub. What does baptism do for those who do not come to faith? I think traditional Reformed thought has been silent or said it does nothing. Federal Vision says baptism brings them into the church, and they partake of Christ non-savingly for a time, looking to make sense of John 15:1-5 and Heb 6:4 ish thereby. I don't find this heterodox, so long as it doesn't lead to the view that the sacraments automatically work salvation, which I don't think it does, inherently. If that is the concern, I can deny baptismal regeneration all day long, that sacraments do not save in themselves, etc. But they are more than a symbol, or we are Zwinglians. They are efficacious means of salvation, as our confessions (Westminster) assume and assert.