Romans 7:1-3
(1) Know ye not, brethren, (for I speak to them that know the law,) how that the law hath dominion over a man as long as he liveth?
(2) For the woman which hath an husband is bound by the law to her husband so long as he liveth; but if the husband be dead, she is loosed from the law of her husband.
(3) So then if, while her husband liveth, she be married 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 married to another man.
Verses 1-6 relate to 6:14, the intervening verses (6:15-23) being a digression raised by the question in 6:15. The statement that a believer identified with Jesus Christ in His death is no longer “under Law” (6:14) should not have surprised Paul’s readers because they were men who know the Law. This statement should not be restricted to Jewish believers in the church at Rome because Gentiles also knew the principle that the Law has authority (kyrieuei, “rules as lord”; cf. 6:9; 14) over a man only as long as he lives. This is a self-evident truth, which Paul then illustrated by marriage. A married woman (lit., “the under-a-man woman”) is bound (perf. tense, “has been bound and stands bound”) to her husband as long as he is alive. But if her husband dies (in Gr., a third-class condition indicating a real possibility) she is released (perf. tense, “has been and stands discharged”) from the law of marriage (lit., “from the law of the man”). She is bound to him by marriage as her husband while he lives, and obviously his death frees her from that marriage.
Then Paul continued the illustration, pointing out that if a wife marries (lit., “if she comes to”) another man while her husband is still alive she is called (future tense, “shall be publicly known as”) an adulteress. Conversely, on the death of her husband she is free from that marriage (cf. 7:2). So she is not an adulteress if she marries (lit., “even though she comes to”) another man. A widow who marries again is not guilty of adultery.
Excerpt from:
Walvoord, J. F., Zuck, R. B., & Dallas Theological Seminary. (1983-c1985). The Bible knowledge commentary : An Exposition of the Scriptures. Wheaton, IL: Victor Books.
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