There is an idiom “when in Rome” that means when you visit or travel to a location that you should try, adopt, or live with the norms of that society. While you are in a country be it your own or one you visit you must follow the laws of that country. Americans when they travel abroad sometimes have a bad reputation because they do not respect the local cultures and rules. I know I appreciate when someone who is visiting my community goes out of their way to understand and acknowledge how we do things.
Paul in his letter to the church in Rome uses this when in Rome idea to make a life changing point about how God works out salvation and restoration of human kind.
Or do you not know, brothers—for I am speaking to those who know the law—that the law is binding on a person only as long as he lives? Romans 7:1 ESV
We all know the law it is written in our hearts and God makes it concreate with the Ten Commandments. Do not lie, do not murder, and so on. While you live on this planet you are bound to the law. When in Rome… The law written in your heart, your conscience, condemns when we fail to meet its expectations. Paul writing to a group that knows Jewish law very well then goes into detail about a specific law regarding adultery.
3 Accordingly, [a woman] will be called an adulteress if she lives with another man while her husband is alive. But if her husband dies, she is free from that law, and if she marries another man she is not an adulteress. Romans 7:3 ESV
Divorce, unfortunately, is common in American culture so much so that many people refuse to even get married because of the pain of the situation. Paul using this as an example shows that when two people are married that they are bound under the law for a life time. Only death of one partner frees the other to remarry. The law is binding as long as we live on this planet. Jesus spoke about this issue when a group questioned him asking if a man had married multiple times over the course of life what wife would he be with in Heaven.
29 But Jesus answered them, “You are wrong, because you know neither the Scriptures nor the power of God. 30 For in the resurrection they neither marry nor are given in marriage, but are like angels in heaven. 31 And as for the resurrection of the dead, have you not read what was said to you by God: 32 ‘I am the God of Abraham, and the God of Isaac, and the God of Jacob’? He is not God of the dead, but of the living.” Matthew 22:29-32 ESV
The laws that make the standard for life on earth and the rules of life on this earth do not apply after death. Death ends the hold of the law on people both in the positive way, marriage, and in the negative way, adultery. In eternity the law will no longer be our master and no longer will we be slaves to the passion it brings up in our hearts.
5 For while we were living in the flesh, our sinful passions, aroused by the law, were at work in our members to bear fruit for death. 6 But now we are released from the law, having died to that which held us captive, so that we serve in the new way of the Spirit and not in the old way of the written code. Romans 7:5-6 ESV
We are married to the law of sin and apart from God. The law points out our sinful passions and inflames them even more. And as long as we live, we are bound to the law of sin and unable to be with God. So, God in his grace and love kills us to free us from the law sin. This is the message of the gospel. We die to ourselves. We are buried with Christ. And we are raised to a new life. A new life bound and now remarried to the Spirit.
4 We were buried therefore with [Christ] 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. Romans 6:4 ESV