For the woman who has a husband is bound by the law to her husband as long as he lives. But if the husband dies, she is released from the law of her husband. So then if, while her husband lives, she marries another man, she will be called an adulteress; but if her husband dies, she is free from that law, so that she is no adulteress, though she has married another man. (Romans 7:2-3)
The law had jurisdiction over a person as long as they lived, as Paul wrote in Romans 7:1.
In Romans 7:2-3 - Paul will make the same point using the specific illustration of marriage.
Death releases the marriage bond.
If the husband dies the woman is no longer bound by that marriage law. As long as there is life, the law is binding. The illustration has simply moved into a more specific area. - McGuiggan, Romans, 201
Even today, when a man and woman are married, they say, “Til death do us part.” Marriage is a bond - or link - that men and women should not separate.
And He [Jesus] answered and said to them [the Pharisees], "Have you not read that He who made them at the beginning 'MADE THEM MALE AND FEMALE,' and said, 'FOR THIS REASON A MAN SHALL LEAVE HIS FATHER AND MOTHER AND BE JOINED TO HIS WIFE, AND THE TWO SHALL BECOME ONE FLESH' [quoting from Genesis 1:27 and 2:24] ? So then, they are no longer two but one flesh. Therefore what God has joined together, let not man separate." (Matthew 19:4-6)
When the husband - or the wife - dies, that marriage bond is severed. The woman whose husband has died is no longer bound in marriage to him.
She can take another husband without being an adulteress. She is no longer in her first marriage because her first husband died.
For the remaining partner in such a situation as Paul described, the marriage was null and void. In the same way, Christians had freedom from the Law, since they had died to it. - Pollard, Truth for Today Commentary, 229
The Bible elevates women and marriage.
When Paul wrote these words, the world’s standards for marriage were drastically different for men and women.
In the Greek and Roman cultures, unconditional faithfulness to marriage was demanded only of women - married men were allowed to have sexual relationships with other unmarried women.
If a married woman was caught being unfaithful to her husband, the man divorced her, and she was not allowed to visit public temples.
In most cultures at that time, a woman had to accept it if her husband committed adultery, while she could be put to death if she did the same thing as her husband.
However, you find in the Bible an elevation of the expectations placed upon both the man and woman in a marriage.
Paul made it clear that under the divine command of God, both the man and the woman are held to the same high standard of behavior (1 Corinthians 5:1-13). - Pollard, Truth for Today Commentary, 229
Marriage is a bond meant to be respected by both men and women and not just thrown away like it’s nothing (Matthew 5:32; 19:9).
Remember Paul’s point: when a woman’s husband died, she was released from that marriage and was free to marry another man.
This illustration is essential to the point Paul is about to make about the law.