“Do you not know that those of us who were baptized into Jesus Christ were baptized into his death?” [Romans 6:3]
Baptism is evidence that we are implanted into Christ, baptized into him. But what interest do we gain in him by being baptized? “His death,” Paul says. If we are indeed baptized into Christ, beyond mere formality, then we are baptized into his death. The apostle gives us an explanation of being baptized into the death of Christ in Romans 6:4, 6. “Therefore we are buried with him by baptism into death, so that just as Christ was raised up from the dead by the glory of the Father, we may also walk in newness of life.
Knowing that our old man is crucified with him, rendering the body of sin without effect, we should not serve sin as a slave anymore.” He is saying, “This is being baptized into the death of Christ, namely, to be dead to sin, to have our sins put to death just as he was put to death for our sins. This was done so that we may be raised up to grace and newness of life, just as he was raised up to glory.” He tells us why we have this baptism into the death of Christ: “Our old man is crucified with him, so that the body of sin might be destroyed,”2 [NT:4957 sustauroo]. It is “crucified with him,” not as to its timing, but as to its cause. We are crucified with him,
meritoriously, in that he procured the Spirit for us to mortify sin;
efficiently, in that from his death virtue blooms to enable us to crucify sin;
representatively, in that we will certainly be crucified to sin, just as he was for our sin.
This is what the apostle means: by his death, Christ destroyed the works of the devil, procured the Spirit for us, and killed the reign of sin in believers in such a way that it will not realize its goal, which is to control and destroy us.
~ John Owen