Though I do not fully agree with Luther on all his baptismal views, this one is outstandingly God-centered – it is still wrestling me around the room as I type.
“We are baptized[;] not because we are certain of our faith but because it is the command and will of God. For even if I were never certain any more of faith, I still am certain of the command of God, that God has bidden to baptize, for this he has made known throughout the world. In this I cannot err, for God’s command cannot deceive. But of my faith he has never said anything to anyone, nor issued an order or command concerning it.”
“True, one should add faith to baptism. But we are not to base baptism on faith. There is quite a difference between having faith, on the one hand, and depending on one’s faith and making baptism depend on faith, on the other. Whoever allows himself to be baptized on the strength of his faith, is not only uncertain, but also an idolater who denies Christ. For he trusts in and builds on something of his own, namely, a gift which he has from God, and not on God’s Word alone. So another may build on and trust in his strength, wealth, power, wisdom, holiness, which are also gifts given him by God. But a baptism on the Word and command of God even when faith is not present is still a correct and certain baptism if it takes place as God commanded. Granted, it is not of benefit to the baptized one who is without faith, because of his lack of faith, but baptism is not thereby incorrect, uncertain, or of no meaning.”
“If we were to consider everything wrong or ineffectual which is of no value to the unbeliever, then nothing would be right or remain good. It has been commanded that the gospel should be preached to all the world. The unbeliever hears it but it has no meaning for him. Are we therefore to look on the gospel as not being a gospel or as being a false gospel? The godless see no value in God himself. Does that mean he is not God?”
In other words, faith wavers, waxes, and wanes, but the objective Word and promise of God do not; Luther said baptism is based on the latter, not the former. The historical context of these statements is important to consider as well – he was writing in response to the Anabaptists of the day, who said baptism didn’t “stick” if a person didn’t have faith. On that basis, the Anabaptists would baptize people again (and again if necessary). The entire tract of Luther, Concerning Rebaptism (from which the above quotes come) is pretty profound and an excellent read.