Baptism into Death
Romans 6:4 (ESV) … “We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.”
“The word ‘baptized’ is not the translation of the Greek word here, but its transliteration, its spelling in English letters. The word is used in the classics of a smith who dips a piece of hot iron in water, tempering it; also of Greek soldiers placing the points of their swords, and barbarians, the points of their spears, in a bowl of blood.… The usage of the word as seen in the above examples resolves itself into the following definition of the word baptizō, ‘the introduction or placing of a person or thing into a new environment or into union with someone else so as to alter its condition or its relationship to its previous environment or condition.’ And that is its usage in Romans 6.
It refers to the act of God introducing a believing sinner into vital union with Jesus Christ, in order that the believer might have the power of his sinful nature broken and the divine nature implanted through his identification with Christ in His death, burial and resurrection; thus altering the condition and relationship of that sinner with regard to his previous state and environment, bringing him into a new environment, the kingdom of God.”
In other words, in this biographical illustration, Paul refers to our baptism into Christ. This is something that happens at conversion so far as our experience is concerned. There are others who maintain, of course, that the baptism referred to here is water baptism and not Spirit baptism. Whichever view is adopted, the fact remains that Paul is driving home the reality of our death with Christ by pointing to a real and actual personal experience.
The second illustration follows. “For if we have been planted together in the likeness of his death, we shall be also in the likeness of his resurrection” (v. 5). The word “planted” here is literally “united together.” Wuest says the word could be used of Siamese twins. Sanday translates it “united by growth” and adds, “The word exactly expresses the process by which a graft becomes united with the life of a tree. So the Christian becomes ‘grafted into’ Christ.” We become vitally united to Him. We share His very life.
In these two illustrations, the one biographical and theological and the other biological, Paul is seeking to convey the remarkable truth that Christ’s death was our death; His burial was our burial; His resurrection was our resurrection. He not only died for me; He died as me! So far as God is concerned, we are already on the resurrection side of the grave and it but remains for us to realize this truth and appropriate it, and victory is assured.
 Phillips, J. (2009). Exploring Romans: An Expository Commentary (Ro 6:1–5). Kregel Publications; WORDsearch Corp.