United to Christ
"If we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. We know that our old self was crucified with him . . . so that we would no longer be enslaved to sin. For one who has died has been set free from sin."
That baptism is the new covenant equivalent of circumcision (Col. 2:11–12) shows us the falsehood of baptismal regeneration. As we see in the case of Abraham and Isaac (Gen. 15:6; 17; 21:1–4), some were regenerated long before their flesh was cut (Abraham) and some were regenerated long after undergoing the rite (Isaac). Similarly, people can be regenerated before or after they are baptized. One is not regenerate and does not have eternal life merely by being baptized. Baptism conveys God's promise, not regeneration itself.
Still, because God's promises are effectual for the elect, and because first-century believers were typically baptized immediately upon coming to faith (see Acts 8:26–40), the Apostles sometimes speak of baptism in a way that connects the sign and the reality more closely than we might be comfortable with, given that we have had to face the error of baptismal regeneration that arose after the Apostles died. Our zeal to counter baptismal regeneration must not drive us to the opposite error of believing that baptism is an empty sign that does not convey any tangible benefits to the baptized. In baptism, God truly confirms His promises in a special way, including His promise to unite believers to Christ in His death and resurrection. Whether one is immersed, sprinkled, or receives baptism by pouring, the imagery of being covered and then uncovered by water depicts the reality of death and resurrection wherein one is covered by the grave and then escapes it.
When the Lord, in His sovereign timing, baptizes us into Christ's death by granting us faith through His monergistic work of regeneration, we enter into a new relationship with sin. Sin has rightful dominion over those who are outside of Christ. In Adam, we chose to reject our Creator for another master—sin—and in God's providence, we became legally bound to that ruler (Rom. 5:12–21). Sin is the Lord's enemy, but He gave it legal rights over us when we chose to serve ourselves instead of God Himself. This was done with the intent of exalting His glory by destroying sin and Satan (Heb. 2:14); still, sin has delegated rights over us in Adam, and these rights exist as long as we live under the sphere of sin's rightful control.
Like any master, however, sin loses all rights over its slaves at the moment of their deaths. When Christ died, we died with Him. When the old man—our sinful selves outside of Jesus—died, so too did any authority sin had over us. When Christ was raised, we were raised with Him to serve willingly a new master, the Lord of glory Himself (Rom. 6:5–7).
Coram Deo
We served the master of sin for a long time, so we are tempted to live the life of the old man, the life of the one whom sin controls. But sin is no longer our master. When we died, sin lost its authority to control us, and we lost the obligation to do whatever it says. We sin when we forget that sin is no longer our rightful master, that we died to any "legitimate" authority it had over us. We are bound to a new Master, and our obligation to Him is holiness.