Sotah 055

1:
On Mishnah Gittin 7:6 (the text of which is of no immediate consequence to our discussion) Rambam comments as follows:-

The exact reason for this decree of the sages is not clear. It may be because of a fear that the new husband will not want his wife to give birth to someone else's child (even though it is known who the father was); it may be because he would not take kindly to his wife suckling the child of another man; there may be some other social reason that is no longer known to us. The fact is that in order to protect the child the sages prohibit this woman's remarriage for 24 months. In order to give force to this decree the sages further enacted that a man who disobeys this decree and marries such a woman must divorce her.

2:
Our present mishnah teaches that if a man, in disobedience to the decree of the sages, marries a pregnant or nursing woman, if he suspects her of infidelity he may not put her to the ordeal of the 'cursing waters' because their liaison is illicit. He must divorce her and she may not collect the money of her Ketubah.

3:
All that we have written so far is the view of Rabbi Me'ir, but it is not halakhah. The majority of the sages recognize the possibility that the new husband may 'set aside' his wife conjugally for the period of 24 months and then take her again for the purposes of intimacies. This kind of 'temporary divorce' is acceptable.

4:
There are other women too marriage with whom may be illicit, but for a different reason. Every adult male is required by Torah law to marry and procreate. The Shulchan Arukh [Even ha-Ezer 1:1] dictates:

The term 'Ayelonit' describes a woman who also displays physical signs of masculinity, who is physically incapable of bearing a child. The same problem is obviously the case with 'an old woman' – a woman who is past the age of childbearing. Rabbi Ovadyah of Bertinoro, in his commentary on our mishnah, explains the term used in our mishnah 'a woman who cannot give birth' as referring to a woman who has drunk an infertility potion. What all these women have in common, of course, is that a man cannot fulfill his duty to procreate with them; therefore Tanna Kamma would prohibit his marriage to them. Rabbi Eli'ezer demurs: in an age where it was permissible for a man to have more than one wife there was nothing to stop this hypothetical man from fulfilling his duty with a fruitful woman as well as being married to an unfruitful one.

A while back we mentioned the institution of Yibbum, levirate marriage. Juan-Carlos Kiel writes:

Following the discussion on Yibbum: the Megillah tells us that Ruth had approached Boaz in the Goren (thrashing place?) where all the labourers gathered for the night. Most probably, someone could have heard and seen… Therefore the Go'el might have accused Ruth and let her off without her rights… and without taking her as a wife.
Since there was a closer relative, her coming to Boaz seems not to have been lawful. Should Ruth have been forbidden for Boaz? The same question regarding Bat-Sheva and David: since he approached her while she was still married, shouldn't she be forbidden to marry with him? (By the way, the goren had as well sacred properties; it is the goren of Aravna on Mount Moriah which was to be the place of the Temple in Jerusalem.)

I respond:

I do not see why Juan-Carlos assumes that sexual intimacies took place between Bo'az and Ruth at the threshing floor. Juan-Carlos himself points out that this was not a private place. Ruth, instigated by Naomi, only wants to put the idea into his head. If I am correct, there is no reason why Bo'az should not have married Ruth. Furthermore, even if sexual intercourse had taken place between Bo'az and Ruth at the threshing floor, in Jewish law this would be no impediment to their marriage.

Of course Bat-Sheva was prohibited to David! Is that not the whole point of Nathan's diatribe against the sinful king?

I do not understand why Juan-Carlos attributes holiness to the threshing-floor of Aravna (which was purchased in order to build the Bet Mikdash on that site.) I think that the sanctity of the site is its being identified with Mount Moriah of the Akedah story.