Returning to the original issue, I'm no biblical scholar, but isn't this entire discussion rendered moot by the "New Covenant"......?
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"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.
Matthew 5:17
A fairly decent interpretation of this can be found at
http://www.mountainretreatorg.net/faq/oldlaw.html.
An excerpt reads:
By fulfilling the law Christ satisfied it's requirements in our place. In other words, the 'required' obedience is accomplished in Him. Therefore, in Christ do we keep all the law faithfully, and cannot be accused. In this way, we are no longer judged by any of the everlasting laws, for we are under the Grace of God. The law doesn't condemn us.
Because we love Christ we try our best not to sin and the law defines what sin is. We are no longer under the penalty of the Law should we sin because Christ fulfilled that for us. However we must avoid sin which means that we must do our best to observe it and seek forgiveness when we break it.
Now the topic that started this tread concerned a wife who later remarried her husband,s bother. Those seem more like laws of social custom and were concerned with the family line being extended. Some laws of this nature did not need to be maintained once their usefulness had run its course. They weren't moral laws which is what God's laws mainly dealt with.
At any rate, MSB's answer is far more succinct and to the point.