https://toldot.com/blogs/akrasilschikov/akrasilschikov_709.html
(Sanhedrin, leaf 22, 1)
The Mishnah proclaims, speaking of the laws of Jewish kings: «...His horse they do not ride, and upon his throne they do not sit, and with his scepter they do not use, nor do they look upon him during the time of his hair cutting, nor then, when he is naked, nor in the bath, as it is said: 'You shall set a king over you, that fear may be upon you...'"
Rabbi Jacob brings the words of Rabbi Yochanan: Avishag the Shunammite is permitted to Solomon /who inherited David's throne/ and forbidden to Adonijah /Solomon's half-brother/. Solomon is permitted, because he is king, and it is allowed for a king to use the scepter /of his predecessor/, but it is forbidden to Adonijah, for he is a mere mortal /though of royal lineage/...
But who is Avishag? The first book of Kings tells about her:
«...And King David reached old age, and they covered him with clothes, but he did not get warm. And the servants said: 'Let them seek for my lord the king a young virgin, and let her stand before the king, and let her be his companion and lie in his bosom, and she shall warm my lord the king.' And they sought for a fair damsel throughout all the coasts of Israel, and found Avishag the Shunammite, and brought her to the king. And the damsel was very fair, and she became the king's companion and ministered to him, but the king did not know her...»
The Gemara continues:
«Avishag said: Let us marry. — He (David) said to her: You are forbidden to me...»
Rashi explains: David means that he already has eighteen wives, and the Torah forbids the king to have more than this number, as it is written: «...Neither shall he multiply wives to himself...»
And here the Shunammite utters a strange and even audacious phrase:
«She said to him: when a thief cannot find an opportunity to steal, he pretends to be honest...»
Avishag suggests that the true reason for refusal lies in David's old age and feebleness, and the pious words are merely an attempt to conceal it.
«He said to them (the servants): let them call for me Bathsheba! And it is written: 'And Bathsheba went in unto the king into the chamber, and the king David was very old, and Avishag the Shunammite ministered unto the king...' Rabbi Judah said in the name of Rava: at that time, Bathsheba changed the bedclothes thirteen times...»
On that day, Rashi explains, David engaged in marital relations with his wife thirteen times in a row.
Why then did David not desire to take Avishag even as a concubine? Why did it become necessary to confront the law and obtain special permission to be alone with an unmarried girl?
There are enough answers at first glance. Firstly, only a young girl who did not know a man could suit the role of a companion.
Moreover, the king knew that he was living his last days, that he was ill and would soon die. By taking Avishag as a concubine, he would condemn her to loneliness, for according to the law, a king's concubine has no right to marry anyone, including royal heirs.
Pitying Avishag, David did not allow himself to take her even as a concubine. Simply serving David, Avishag, though imposing certain restrictions on herself and unable to marry an ordinary man, could at least become the wife of Solomon, the future king, David's son.
But here's another question: how could such a righteous woman as Avishag speak so boldly to the king and, even allegorically, liken him to a thief, and even reproach him for his old age – isn't this perceived as a direct mockery?
As strange as it may sound, there are righteous «deceivers» and righteous «thieves».
This refers to «stealing» away the evil impulse that torments a person from without and within, and to «lying» in order to do a good deed.
Such was David. Every time he prepared to leave his home, he told himself: «I am going for a walk in the garden...», or: «It would be nice to go to the bathhouse...» With these words, he left the palace gates, but on the way, encountering the House of Study, he suddenly turned and disappeared into the doors, mingling with the crowd of Sages, where the evil impulse could not follow!
Why did David behave like this? What compelled him to resort to such strange and seemingly «naive tricks»?
The answer is very simple. Satan or the evil nature of man exerts incredible efforts to prevent a person from performing good deeds. The higher the spiritual level, the greater the level of resistance...
If David, whose Torah study had immeasurable spiritual value, had openly stated that he was going to the House of Study, Satan would have moved mountains to interfere. But by convincing himself that he was going to some insignificant place or for idle pastime, David misled the evil impulse, which then did not present any obstacles.
In his pursuit of good, David had to resort to such tricks time and again and, like a «thief,» deceive the «guard» stationed at the treasure house of good deeds.
This characteristic of the king was what Avishag had in mind, likening David to a «thief.»
But what did this have to do with her?
Avishag believed that the evil impulse did not want David to live a marital life, where the king would ascend to a high spiritual level, so it deprived David of physical desire in his old age.
To deceive the evil impulse once again, Avishag thought, David used her, taking her without a Ktuba /marriage contract/ and Kiddushin /betrothal/ under the pretext of needing a living warmth.
In order to incline David to forbidden cohabitation, the evil impulse would be willing to restore lost strength to the king, and he would then use this «fire» to continue marital life in purity and holiness.
Avishag eagerly supported the «game» at first, but then, desiring to ascend to a higher spiritual level with David, she offered herself as a wife.
Receiving a refusal under a quite plausible pretext, Avishag concluded that the king's «experiment» had failed and hinted that by failing to deceive Satan this time, David was deceiving himself by distancing himself from sin under the pretext of supposedly being unable to add another wife, when the true reason was physical weakness.
To demonstrate that Avishag was mistaken, David summoned Bathsheba.
Now the following remains unclear: why is it so important for the role of a «companion» to be performed by the most beautiful and attractive girl in Israel, why couldn't an ordinary-looking girl fit this role, and why did David need to subject himself to voluntary or involuntary testing if he did not intend to marry his «companion»?
To answer, one must recall the past. David until the very last day tried to rectify his mistake with Bathsheba. He spent his whole life repenting that he succumbed to the evil impulse, not waiting for Bathsheba, «destined to him as a wife since the Six Days of Creation,» to become unquestionably permissible to him.
No wonder the king wished for the most beautiful of Israel's daughters to occupy the position of his attendant.
David hoped that this would artificially recreate the situation in which he once faltered but this time would remain at the proper level...
Avishag did not suspect this. She believed that she was taken to the king to eventually become his wife. That's what she asked for.
When David refused, explaining the true meaning of her service, Avishag did not believe him. She thought that, aged, David lacked the former strength to rectify what he did with Bathsheba and resembled a thief who, unable to steal, pretends to be innocent.
She could be sent away, Avishag thought, replaced by someone else willing to play the role of a simple «companion.»
What she heard prompted David to summon Bathsheba and show that Avishag was mistaken and her role in rectifying the king was invaluable. [1]
[1] Melakhim-1,1
[2] Devarim,17
[3] Ben Yehoyada
[4] Ibid