Lutherans believe that the Bible teaches that a person is saved by God’s grace alone through faith in Jesus Christ alone.
The Bible tells us that such “faith comes by hearing” (Rom. 10:17). Jesus Himself commands Baptism and tells us that Baptism is water used together with the Word of God (Matt. 28:19-20).
Because of this, we believe that Baptism is one of the miraculous means of grace (another is God’s Word as it is written or spoken), through which God creates and/or strengthens the gift of faith in a person’s heart (see Acts 2:38; Acts 22:16; 1 Peter 3:21; Gal. 3:26-27; Rom. 6:1-4; Col. 2:11-12; 1 Cor. 12.13).
Terms the Bible uses to talk about the beginning of faith include “conversion” and “regeneration.” Although we do not claim to understand fully how this happens, we believe that when an infant is baptized God creates faith in the heart of that infant.
We believe this because the Bible says that infants can believe (Matt. 18:6) and that new birth (regeneration) happens in Baptism (John 3:5-7; Titus 3:5-6). The infant’s faith cannot yet, of course, be verbally expressed or articulated by the child, yet it is real and present all the same (see e.g., Acts 2:38-39; Luke 1:15; 2 Tim. 3:15).
The faith of the infant, like the faith of adults, also needs to be fed and nurtured by God’s Word (Matt. 28:18-20), or it will die.
Lutherans do not believe that only those baptized as infants receive faith. Faith can also be created in a person's heart by the power of the Holy Spirit working through God's (written or spoken) Word.
Baptism should then soon follow conversion (cf. Acts 8:37) for the purpose of confirming and strengthening faith in accordance with God's command and promise. Depending on the situation, therefore, Lutherans baptize people of all ages from infancy to adulthood.
The LCMS does not believe that Baptism is ABSOLUTELY necessary for salvation. All true believers in the Old Testament era were saved without baptism. Mark 16:16 implies that it is not the absence of Baptism that condemns a person but the absence of faith, and there are clearly other ways of coming to faith by the power of the Holy Spirit (reading or hearing the Word of God).
Still, Baptism dare not be despised or willfully neglected, since it is explicitly commanded by God and has His precious promises attached to it. It is not a mere “ritual” or “symbol,” but a powerful means of grace by which God grants faith and the forgiveness of sins.
From Luther's Small Catechism:
As the head of the family should teach it in a simple way to his household:
What is Baptism?
Baptism is not just plain water, but it is the water included in God’s command and combined with God’s word.
Which is that word of God?
Christ our Lord says in the last chapter of Matthew: “Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit.” (Matt. 28:19)
What benefits does Baptism give?
It works forgiveness of sins, rescues from death and the devil, and gives eternal salvation to all who believe this, as the words and promises of God declare.
Which are these words and promises of God?
Christ our Lord says in the last chapter of Mark: “Whoever believes and is baptized will be saved, but whoever does not believe will be condemned.” (Mark 16:16)
How can water do such great things?
Certainly not just water, but the word of God in and with the water does these things, along with the faith which trusts this word of God in the water. For without God’s word the water is plain water and no Baptism. But with the word of God it is a Baptism, that is, a life-giving water, rich in grace, and a washing of the new birth in the Holy Spirit, as St. Paul says in Titus, chapter three: “He saved us through the washing of rebirth and renewal by the Holy Spirit, whom He poured out on us generously through Jesus Christ our Savior, so that, having been justified by His grace, we might become heirs having the hope of eternal life. This is a trustworthy saying.” (Titus 3:5–8)
What does such baptizing with water indicate?
It indicates that the Old Adam in us should by daily contrition and repentance be drowned and die with all sins and evil desires, and that a new man should daily emerge and arise to live before God in righteousness and purity forever.
Where is this written?
St. Paul writes in Romans chapter six: “We were therefore buried with Him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.” (Rom. 6:4)
From Luther’s Small Catechism © 1986 Concordia Publishing House, cph.org