On Baptism

[We] ought to regard baptism as much greater and more precious because God has commanded it. What is more, it is performed in his name. So the words read, "Go, baptize," not "in your name" but "in God's name." Tobe baptized in God's name is to be baptized not by human beings but by God himself. Although it is performed by human hands, it is nevertheless truly God's own act. [...]

Note the distinction then: Baptism is a very different thing from all other water, not by virtue of the natural substance but because here something nobler is added, for God himself stakes his honor, his power, and his might on it. Therefore it is not simply a natural water, but a divine, heavenly, holy, and blessed water - praise it in any other terms you can - all by virtue of the Word. [...]

"The one who believes and is baptized will be saved," that is, faith alone makes the person worthy to receive the saving, divine water profitably. Because such blessings are offered and promised in the words that accompany the water, they cannot be received unless we believe them from the heart. [...]

Baptism is simply water and God's Word in and with each other; that is, when the Word accompanies the water, baptism is valid, even though faith is lacking. For my faith does not make baptism; rather, it receives baptism. Baptism does not become invalid if it is not properly received or used, as I have said, for it is not bound to our faith but to the Word.

-- Martin Luther, "Fourth Part: Concerning Baptism", Large Catechism