How could Saul do this with David’s wife? The text even emphasizes the problem, calling her אשת דוד. One explanation might be that, in fact, Saul sinned. The Midrash Tehillim attributes the advice to our old adversary, Doeg:
However, there’s an important point to be made about תנ״ך. ספר שמואל is written as a ספר נבואה, not just as a history book. We have mentioned before that the actions of those that the נביא or חז״ל identify as צדיקים are assumed to be consistent with the Torah, unless they are specifically called out as wrong (such as David and Bat Sheva). While we can assume Doeg was sinning, we are going to try to justify the actions of Saul and David, and even can use the stories here to learn הלכה למעשה. The questions at hand are ones that come up in real life, and this incident is quoted by the פוסקים in deciding matters of marriage and adultery. We will therefore be going further afield than usual, quoting not just the בעלי פשט but also those who focus on actual הלכה.
It goes without saying, so I’m going to engage in a little paralipsis: I make no claim to know anything and nothing I say can be used for a final halachic decision. CYLOR.
One solution is to say that David was not at that time married to Michal. We know that חז״ל said that every Israelite soldier would give his wife a get before going to war, to avoid a possible עגונה problem:
But there’s a huge problem with this answer, from David’s later behavior:
If he divorced Michal, he cannot remarry her after she is married to Palti:
And the Radak is aware of the problem:
So if the divorce was invalid, why bring it up? It explains why Saul would feel it permissible to have Michal marry another, and why Michal would go along with it (at least, we have no evidence that she protested, and Palti is called אישה). But this explanation is rather forced; there’s no evidence for it in the text. And it leaves unanswered another textual question: why does David call her מיכל אשר ארשתי לי במאה ערלות פלשתים? Why bring that up?
Before we get to that, I want to mention one other solution to the problem, from the Gemara:
While this makes Palti a great צדיק, it doesn’t really solve the problem of adultery, as Tosaphot points out (in a discussion of immorality with both parties fully clothed):
What does תוספות mean by סבר כשאול? The gemara’s solution to the question of how Saul could give away Michal centers on David’s comment about the מאה ערלות פלשתים:
So Saul had a halachic justification for claiming that David was not truly married to Michal, even though the final פסק is that he was married (similar to Radak’s explanation about the get, above). The פוסקים use this as the “hook” to explain our story.
But first, we need to look at another adultery in תנ״ך: Esther. The gemara claims she was in fact married to Mordechai:
Which brings up the question of how she could allow herself to be married to Achashverosh:
This brings up the fascinating question of whether Esther was right to do what she did; commit a mortal sin to save the entire Jewish people:
And the Rashba’s famous comment:
But it would take us too far afield to go into that question. We are left with the gemara’s unambigous conclusion that אשת ישראל שנאנסה מותרת. The Rashba puts this together with the discussion above about Saul’s halachic reasoning to bring what I think is an amazing חידוש (the Radak comes to a similar conclusion with respect to his proposed invalid get):
Note that Michal is permitted to David whether or not she went willingly to Paltiel. We will look more at her mindset toward her first husband when we deal with her return על אתר in שמואל ב.