Actually, that was not the early Church criterion. The early Church considered all works of Apostles as inspired and tose were the works that were read out loudly in churches (see also my post 2111).
We only have a promise of salvation through baptism
The Gospels say that only those who are baptized and believe shall be saved; but those who do not believe shall not be saved. Therefore, baptism is not the promise of salvation. Likewise, a child cannot believe even if he or she is baptized.
Baptism restores our free will so that we can choose. Baptism is not a some kind of a "spell" that saves us. It is grace of the Holy Spirit that cleanses (washes) us spiritually. Without baptism, our judgemnt is occluded and distorted. Those who are baptized and sin do so of their own choice.
You are right, the criteria for canonicity are different; I simply meant correctness of a particular statement.
baptism is not the promise of salvation
Baptism is a part of the promise, but not the entire promise; this is why I said "through" not "with".