Romans chapters six and seven mention two things from which death makes one free. "For he who has died has been freed from sin" (Rom. 6:6), and "if her husband dies, she is free from that law, so that she is no adulteress, though she has married another man" (Rom. 7:4). Notice the sixth chapter first. Paul said we are baptized into the death of Christ and into (our) death (Rom. 7:3,4). Before we can be joined to Christ, we must die to sin. That takes place when we are buried into His death, or His blood (Rev. 1:5), and "raised to walk in newness of life." The new life follows the burial. When a person is baptized into Christ's death, the "old man was crucified with Him" (Rom. 7:6), he is "freed from sin" (Rom. 7:7), or he is "set free from sin" (Rom. 7:18). The man who was dead in sin (Eph. 2:1,5), has died to sin and been raised to a new relationship with Christ.
Adam Clarke, who believed in sprinkling, made this comment on Romans 6:4: "It is probable that the apostle here alludes to the mode of administering baptism by immersion, the whole body being put under the water, which seemed to say, the man is drowned, is dead; and when he came up out of the water, he seemed to have a resurrection to life; the man is risen again; he is alive!" I would disagree with his word "probable," since that is exactly what the passage says, but he had the right idea about what happens when one is buried in baptism. The man who was dead in sin, is buried and dies to sin, because there he receives the benefits of Christ's blood and he arises from his former state of spiritual separation to being united with Christ.
In the seventh chapter, Paul uses the marriage relationship to show the believer's relationship to the Law. He said a woman is bound to her husband as long as he lives, "but if the husband dies, she is released from the law of her husband" (Rom. 7:2). If she marries another, while her husband lives, she is an adulteress. (This does not discuss the exception in Matthew 19. It is talking about the general rule.) The application of the example is that we must be "dead to the law" before we can be "married to another, even to Him who was raised from the dead" (Rom. 7:4). What we are dead to, we are separated from!
Just as dead to sin means separated from it, dead to the law means separated from it. We can no more be under two Testaments at the same time than we can be married to two people, or joined to sin and to Christ at the same time. Death to sin frees us to walk a new life, death to the Law frees us from the Old Testament, and a companion's death frees us to marry another.