In Romans 7, the Lord’s apostle expounds on the significance of the Law of Moses in relation to the Lord’s New Covenant. In this exposition, he speak of marriage and adultery. To the Jew, to obey a law other than the Law of Moses, one was guilty of adultery, and adultery is punishable by death (cf. Deut. 17:1-5). In fact, this theme is seen throughout the writings of the prophets.
To those of Jewish persuasion, Paul knew he had a case to make. This he does in his letter to the church at Rome, just as he did when went into the synagogues each Sabbath day when the local Jewish community gathered for study of the Torah and Prophets (cf. Acts 17:3).
As long as the Law of Moses was sanctioned by God and in active force, for one who was a Jew, to obey something that was different than the Law of Moses was to be liable to punishment. However, if the Law of Moses was no longer sanctioned by God and in active force, to obey the New Covenant not only relieved one from the punishment of death, but actually liberated those who obeyed from the heart (6:16-18) from sin, something they could not be relieved from by the Law of Moses (Acts 13:39).
Using the illustration of marriage, Paul makes his point. A woman is married, but when her husband dies she is no longer married (but a widow). According to the Lord, the Law of Moses died (Colossians 2:14); thus, those who “marry” the New Covenant, now live life with a new groom.