Submission to public baptism is a visible sign of becoming a Christian, and joining the one Church, the Body of Christ.
You made that up.
"witness to the world ....testimony...symbol...sign " and all that jazz..
To those who agree that water baptism does not save, but it should be practiced as a " testimony", a "witness to the world" of our salvation, I ask:
Where was the lost "world"(or anyone, for that matter) in the 3 most notable baptisms in the book of Acts? Who was present in Acts 8 when the Ethiopian eunuch was baptized, except Philip? Just the chariot driver? Who was present when Saul(Paul) was baptized in Acts 9? Only Anias? Who was present when the Philippian jailor was baptized in Acts 16? Only his family? Nowhere in scripture will you find any verse that tells of water baptism as a testimony to "the world", lost or saved.
From a sensical point of view, would not the water ritual be a rather poor method to witness to the lost of your salvation? Just how is a sopping wet person a testimony to 1 Cor. 15:1-4 KJV, Eph. 2:8-9 KJV............? A witness has a testimony, i.e., he/she speaks or writes of what has taken place. And just how does wet clothes, wet hair.....do that?
And how is a ceremony, that is, in most cases, performed within the walls of a church building, with mostly believers present, not the lost, effective as a testimony to the lost, i.e., most of the audience is saved! If those that contend that it should be done as a testimony to the lost, then, if they were intellectually honest, then they would go down to the nearest stream/lake/pond and start "dunking away" until the tadpoles knew their social security number.
The basic idea behind the concept of baptism is identification=placing or putting something into another substance, performing an action, with the resulting purpose of a change in the state of the item from its previous condition=change in identity, change in condition, change in status.
Symbol? No one was buried in water. The Lord Jesus Christ was not buried in a liquid grave, but in rocks, and buried when dead. In contrast, the "dry baptismal" candidate is buried as soon as he has received life!