“Baptism is an ordinance of the New Testament, ordained by Jesus Christ, to be to the person baptized a sign of fellowship with Christ in his death and resurrection, of being grafted into him, of remission of sins, and of giving up oneself to God, through Jesus Christ, to live and walk in newness of life.” 1689 Second London Baptist Confession, Chapter 29, paragraph 1.
Baptism is not a word of man, it is a word of God to the one being baptized. This is why baptism can be carried out in a private setting, as it is in the Bible. In baptism the Christian receives God's promises and blessing - not of salvation, but the seal of God upon faith.