1. A woman is married to one man. She is not committing adultery.
2. A woman's husband dies, and she marries another man. She is not committing adultery.
3. A woman is married to two men at the same time. She is committing adultery.
Romans 7:1-6
1 Know ye not, brethren, (for I speak to those who know the Law,) how that the Law hath dominion over a man as long as he liveth?
2 For the woman who hath a husband is bound by the Law to her husband so long as he liveth; but if the husband be dead, she is released from the Law of her husband.
3 So then if, while her husband liveth, she be joined to another man, she shall be called an adulteress: but if her husband be dead, she is free from that Law; so that she is no adulteress, though she be joined to another man.
4 Wherefore, my brethren, ye also are become dead to the Law by the body of Christ; that ye should be joined to another, even to Him who is raised from the dead, that we should bring forth fruit unto God.
5 For when we were in the flesh, the sinful passions, which were by the Law, did work in our members to bring forth fruit unto death.
6 But now we are released from the Law that being dead wherein we were bound; that we should serve in newness of the Spirit, and not in the oldness of the letter.
Since Christians have been "released from the Law" (Romans 7:6) they are no longer under any obligation to the laws of the Old Covenant. Those who claim to be Christians and say any (or all) of the Old Covenant laws must be obeyed by a Christian commit spiritual adultery (see point #3 above). If they were really Christians, they would be subject only to the laws of the New Covenant, and not remain married to the laws of the Old Covenant.
BDAG (3rd Edition): to cause the release of someone from an obligation (one has nothing more to do with it), be discharged, be released. In our lit. pass. καταργοῦμαι ἀπό τινος of a woman upon the death of her husband κατήργηται ἀπὸ τοῦ νόμου τοῦ ἀνδρός Ro 7:2. Of Christians κ. ἀπὸ τοῦ νόμου be released fr. the law vs. 6. (katargeō, the boldface and underlined are mine)
2. A woman's husband dies, and she marries another man. She is not committing adultery.
3. A woman is married to two men at the same time. She is committing adultery.
Romans 7:1-6
1 Know ye not, brethren, (for I speak to those who know the Law,) how that the Law hath dominion over a man as long as he liveth?
2 For the woman who hath a husband is bound by the Law to her husband so long as he liveth; but if the husband be dead, she is released from the Law of her husband.
3 So then if, while her husband liveth, she be joined to another man, she shall be called an adulteress: but if her husband be dead, she is free from that Law; so that she is no adulteress, though she be joined to another man.
4 Wherefore, my brethren, ye also are become dead to the Law by the body of Christ; that ye should be joined to another, even to Him who is raised from the dead, that we should bring forth fruit unto God.
5 For when we were in the flesh, the sinful passions, which were by the Law, did work in our members to bring forth fruit unto death.
6 But now we are released from the Law that being dead wherein we were bound; that we should serve in newness of the Spirit, and not in the oldness of the letter.
Since Christians have been "released from the Law" (Romans 7:6) they are no longer under any obligation to the laws of the Old Covenant. Those who claim to be Christians and say any (or all) of the Old Covenant laws must be obeyed by a Christian commit spiritual adultery (see point #3 above). If they were really Christians, they would be subject only to the laws of the New Covenant, and not remain married to the laws of the Old Covenant.
BDAG (3rd Edition): to cause the release of someone from an obligation (one has nothing more to do with it), be discharged, be released. In our lit. pass. καταργοῦμαι ἀπό τινος of a woman upon the death of her husband κατήργηται ἀπὸ τοῦ νόμου τοῦ ἀνδρός Ro 7:2. Of Christians κ. ἀπὸ τοῦ νόμου be released fr. the law vs. 6. (katargeō, the boldface and underlined are mine)