The Online Etymology Dictionary
baptize (v.), from Old French batisier (11c.), from Latin baptizare, from Greek baptizein “immerse, dip in water,” also figuratively, “be over one’s head” (in debt, etc.), “to be soaked (in wine);” in Greek Christian usage, “baptize;” from baptein “to dip, steep, dye, color,” from PIE root *gwabh- “to dip, sink.” Christian baptism originally consisted in full immersion. Related: Baptized; baptizing.
We can see from the etymology of the word that it has a two part meaning. The first is to “dip”, “submerge”, or “immerse” in water. The other is to “soak (in wine)”, to “dye”. If one dyes by soaking in wine, what color is it being dyed? Red, like blood. The imagery of baptism by water is a cleansing, a purification, to be washed clean. The imagery of being soaked in wine should bring to mind the image of Christ in His Passion, soaked in blood.
In Jewish Scriptural lore, baptism by water evokes the image of the flood waters cleansing the earth of the iniquities of man, as well as the waters of the Red Sea saving the Hebrews from the oppression of Egypt, and destroying the Egyptian army. It is an image of death and rebirth, of annihilation and recreation, of salvation from slavery to freedom.
This imagery carries over into Christianity, but we also have the imagery of Christ’s baptism in His own blood. And again, the Red Sea is what color? Baptism, then, is primarily an act of death and rebirth. In it we die to sin, and are reborn into the life of Christ.
The life of Christ is everlasting, and is proved in the Resurrection. Christ’s Resurrection is the promise of our own resurrection in Him. We are the dead, and Christ was Baptized for us, who are the dead.
Here, Paul may be speaking of Martyrdom, in imitation of our Lord, for the sake of those who still walk in darkness. Paul is arguing here for the Resurrection of the dead. If the dead do not rise, what good is it to suffer and die for others?
Christ is our proof. In His Resurrection, we know that His sacrifice on the cross has power and meaning. Therefore, we know that our own sufferings and martyrdoms, our own deaths united to His, share in the same power and meaning to conquer death as His.
… This is how I would read the passage, anyway.