I, Jody, take you, John, to be my wedded husband. To have and to hold, from this day forward, for better, for worse . . . ‘Till death do us part.”

(stylegrace.com)
Sealed with a kiss, this vow—in the covenant of marriage—is valid as long as the husband is alive.
Paul’s readers understood that a violation of this law would disgrace Jody as an adulteress. If her husband dies, however, she is free to marry another man.
This is the picture Paul gives us to compare Christians and the Law. Not only do believers die to sin, but also to the Law, thus cancelling the Law’s “lordship” or claim over the believer (vs. 4).
Similar to the picture of baptism, death to sin begins when the believer places his/her trust in Christ. By identifying with the crucified Christ and joining in union to Him, the resurrected Christ becomes the believer’s new “husband”. The Holy Spirit enables the believer to produce good fruit for God.
So What?
Because of Christ’s sacrifice, the way to God is open through faith. No longer trying to earn salvation through an external code of law keeping or following Christian customs, the believer is free to serve God with a new heart out of love and gratitude.