I'm not sure that's true, as most Christian denominations accept that the thief on the cross was saved without (physical) baptism.
Right, which is an example of baptism not being absolutely necessary for salvation; not that baptism isn't efficacious. Baptism is still Baptism and God's promises attached to Baptism are still true.
Ordinarily a child is born vaginally. But there are cases where a child is born via cesarean. The extraordinary doesn't negate the ordinary. Both a child born vaginally and a child born via a cesarean are equally
born.
The example of the thief on the cross doesn't negate what Baptism exists for; just Baptism as the ordinary means of God appropriating the work of Christ to us doesn't mean the thief on the cross isn't saved.
These sorts of absolutist ways of thinking aren't very helpful, because reducing salvation to a kind of formula doesn't work--salvation is God's work to rescue us, and He has revealed to us that salvation is found in Christ alone through His death and resurrection, and that through the preaching of the Word and the Sacraments the God acts to appropriate Christ's work to us; but salvation isn't formulaic. Some people were born into the faith, receiving baptism as infants, and have grown up as believing Christians. Some people became Christian late in life when they heard the Gospel preached to them. Some people heard the Gospel preached to them while young, but it did not take root until much later in life.
Scripture is clear that Baptism is efficacious--it
does what it
signifies. This, however, does not mean that merely not being baptized is a guarantee that one is damned, nor does it mean that simply having been baptized that one will always hold fast to the faith which they were given. There will be people who received baptism and then walk away from the faith; and there will be people who heard the Gospel but never had the opportunity to be baptized (either they were unaware of its importance to no fault of their own, or perhaps their life is tragically cut short before receiving it).
This is why we must understand that Baptism is Gospel, not Law. Baptism is about God's grace, not God's harsh commandments; Baptism isn't salvific because it is an act of obedience on our part, Baptism is salvific because God graciously takes hold of us in Baptism and unites us to Christ and adopts us as children. It is God who is at work in His Sacraments, not us. Just as it is God who is at work in the preaching of the Word, not us.
For it is by grace alone that we are saved, through faith, and this is not of ourselves, it is the gift of God.
-CryptoLutheran