This is an excerpt from Luther’s Large Catechism, in the Book of Concord.
“Comprehend the difference, then, that Baptism is quite another thing than all other water; not on account of the natural quality but because something more noble is here added; for God Himself stakes His honor, His power and might on it. Therefore it is not only natural water, but a divine, heavenly, holy, and blessed water, and in whatever other terms we can praise it, all on account of the Word, which is a heavenly, holy Word, that no one can sufficiently extol, for it has, and is able to do, all that God is and can do (since it has all the virtue and power of God comprised in it).
“Hence also it derives its essence as a Sacrament, as St. Augustine also taught. That is, when the Word is joined to the element or natural substance, it becomes a Sacrament, that is, a holy and divine matter and sign. Read more about Theology Thursday - Luther on Baptism