Baptism is not just plain water, but it is the water included in God’s command and combined with God’s word.
Baptism works the 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.
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.