But our know-it-alls, the new spirit people, claim that faith alone saves and that human works and outward forms contribute nothing to this. We answer: It is of course true that nothing in us does it except faith, as we shall hear later. But these blind leaders of the blind refuse to see that faith must have something in which it believes, that is, something it clings to, something on which to plant its feet and into which to sink its roots. Thus faith clings to the water and believes Baptism to be something in which there is pure salvation and life, not through the water, as I have emphasized often enough, but because God’s name is joined to it…. If follows from this that whoever rejects Baptism rejects God’s word, faith, and the Christ who directs us to Baptism and binds us to it (Larger Catechism, 1978, pp. 101-102).
If Luther actually doubted the salvation of infants or miscarried children who died before they were baptized, or of converts who died before baptism, I would say that his views are problematic. However, his explanation quoted above does not necessitate such superstitious fears, takes the Biblical data seriously, and shows how baptism fits in Protestant soteriology.
God says that baptism signifies his promise, “I will be your God and you will be my people.” Believing what God says is not superstition or works-salvation, but simply faith. It is the only rational alternative to insisting on salvation by new revelations. If God does not reveal himself and His son in Word and Sacrament, then why even have sacraments, the Bible, or preaching?
Luther’s statement reminds me of the great Reformed theologian, Francis Turretin, who wrote:
Although the sacraments are external means and instruments applying (on the part of God) the promise of grace and justification, this does not hinder faith from being called the internal instrument and means on the part of man for receiving this benefit offered in the word and sealed by the sacraments [16.7.20].
The question is not whether faith alone justifies to the exclusion either of the grace of God or the righteousness of Christ or the word and sacraments (by which the blessing of justification is presented and sealed to us on the part of God), which we maintain are necessarily required here; but only to the exclusion of every other virtue and habit on our part…. For all these as they are mutually subordinated in a different class of cause, consist with each other in the highest degree [16.8.5].