Why was David's first act after returning to separate his wives?
Malbim (based on Yerushalmi; refer to 20:3:5:1 and the note there): He showed that they were forbidden to him, because Avshalom was a commoner. Even though Yisrael chose him, they may not rebel against David's kingship and choose another king. This will be a sign how David will deal with Sheva ben Bichri and those who rebel now. He will treat them like rebels!
What is "Beis Mishmeres"?
Radak: It is a house where they will be guarded.
What is the meaning of "Tzeruros"?
Radak: They were tied; they had no Heter [to any man].
Radak citing Targum Yonasan: They were guarded. He likewise translated "Tzur Te'udah" (Yeshayah 8:16) as Ta'ar (guarded).
Why were they called "Almanos Chayos"?
Radak (from Yerushalayim Sanhedrin 2:3): They were like widows whose husbands are alive, for someone else may not use (marry) what the king used.
Why were they like widows? Why did David not have Bi'ah with them?
Radak: It is because his son had Bi'ah with them. Rabanan of Kisarin (Yerushalmi Sanhedrin 2:3) - a commoner's Kelim (wives), which a commoner used, a king may not use them. Kelim of the king, which a commoner used, all the more so the king may not use them 1 !
R. Yudah bar Pazi (Yerushalmi Sanhedrin 2:3): This teaches that David used to [command them to] braid their hair and adorn them and enter them in front of him every day, and he said to his Yetzer ha'Ra "you desired something forbidden to you. I swear, I will make you desire something permitted to you" (and deny it from you)! Sha'arei Teshuvah (1:34) - this was to atone for the episode of Bas Sheva.
Korban ha'Edah: A king may not marry a commoner's widow. We find that David married Avigayil and Bas Sheva! Parshas Derachim - David did not have the status of a king when he married Avigayil, so she was permitted to him even after he was considered king. Radvaz (7:29) suggests that one who rebels against the king, his wife is permitted to the king. Machaneh Chayim 1:16 answers that a Hedyot's use forbids only if it is b'Isur, whether she was of a commoner or of a king' at the time. Meshech Chachmah (Nitzavim 30:2) says oppositely. A commoner's use forbids to a king only if it was b'Heter. Rabanan of Kisarin permit Mefutas Aviv; Avshalom was considered a king, so the Pilagshim were permitted to him, so they became forbidden to David. R. Yudah bar Pazi (refer to 20:3:5:2) forbids Mefutas Aviv, so even if Avshalom was king, they were forbidden to him, so they were permitted to David.
One opinion in the Yerushalmi holds that the Pilagshim were permitted to David; he refrained from them to afflict his Yetzer ha'Ra. How could he withhold Onah (intimacy at the proper time) from them?
Machaneh Chayim (1:18): Pilagshim have no Kidushin; there is no Chiyuv of Onah.
Yefas To'ar (Yerushalmi Sanhedrin 2:3): They pardoned 1 their Onah. Machaneh Chayim (2 EH 41) - because even if he would divorce them, they could not remarry, so they did not lose from this. 2
Meshech Chachmah (Devarim 30:2): Since he did not sin regarding their Bi'ah with Avshalom, he was not concerned for their Igun (inability to have intimacy with any man). 3
Bava Metzi'a 51a: If one was Mekadesh a woman on condition to be exempt from Onah, the stipulation is void, for she cannot pardon bodily pain (Rashi)! That is when she pardons for the entire marriage. On any particular occasion, she can pardon. (PF)/
He retracted from what he wrote above that a Pilegesh has no Kidushin, and there is no Chiyuv Onah (refer to 20:3:5:1). (PF)
Meshech Chachmah: David could not refrain from Bas Sheva or divorce her, even though that would have been the ideal Teshuvas ha'Mishkal, for then her Igun would result from his negligence. (Since his Pilagshim did not sin, why may he afflict them, even if he was blameless for Avshalom's act? Also, Avshalom's act was due to (punishment for) David's sin (12:11)! - PF)
