I understand and agree with Gold Dragon's original statement. The irony is that Baptists are the most adament amoung Christian groups about how baptism must been done but then turn around and argue that baptism means the least (among other christian groups) in terms of what it is or accomplishes. You would think that a group like the presbyterians, who some would argue baptism adds the child into the new covenant (albeit not into savlation) would be more adament about exactly how it must been done.
Piper's move has been discussed on quite a few forums across the web already. I happen to agree with him though First of all I think our modern day concept of memborship is somewhat extra-biblical. In the 1st century everyone who was a believer at all was a member of the body of Christ and whatever local church was close by. When Paul sent Timothy to a church for several years, he didn't need to transfer his memborship! But more importantly, I find it interesting that you would make the gate to your church more narrow then God makes the gate into enternal life. Anyone, who believes in Jesus is saved, even presbyterians. Yet while God says they are part of the Body of Christ, we say they can't be part of our local body. Does that make sense to anyone? In practicality, we do it to preserve our theological differences and maintian and teaching distintives, which is fine. But the funny thing is that I could attent a church for years yet never be a "member" because I don't agree with some defining theological point. That, I call, extra-biblical. Is there any example in the NT where people attending the worship gatherings of the local church, where actual believers in Jesus and part of the body of Christ, yet were not considered part of that local church.
Finnally, as a side note on Piper. I think his reasoning is that it is a Shame that no presbyterians can't join his church, despite the fact that his theology and worship are very similar, but any arminian and even unchurched and untaught non-denom Christian can join who are probably on polar ends of the planet with the elder's teaching.