Paul uses the example of marriage to illustrate a deeper spiritual truth about the law and our relationship to it. In the context of marriage, a woman is legally bound to her husband as long as he is alive. If she engages in a relationship with another man while her husband lives, she is considered an adulteress. However, if her husband dies, she is no longer bound by that marriage law and can marry another man without being considered an adulteress. This analogy is used to explain how the law binds us in a similar way.
In the broader context of Paul's letter, he is addressing how believers are bound to the law until they are released through Christ. Just as death frees the woman from the law of marriage, Christ's death and resurrection free believers from the law's binding power. This freedom allows Christians to live a new life, guided by the Spirit rather than the old written code. Paul is emphasizing that through Christ, believers are no longer under the law's condemnation but are free to pursue a life of righteousness and grace.