What is the meaning of "Asher Hechinani"?
Malbim: He promised to me serenity.
What is the meaning of "Asah Li Bayis"?
Rashi: A house of kingship, like He said via Nasan.
Malbim: Also my descendants will rule after me.
Why did Shlomo see a need to kill Adoniyahu?
Abarvenel (25): Adoniyahu was Chayav Misah for rebelling, i.e. declaring himself king, in David's lifetime. He knew this, and asked Shlomo to swear that he will not kill him (1:51). Shlomo did not swear; he pardoned him on condition that he not repeat his folly. Asking for Avishag nullified the pardon.
Malbim: Since Hashem said that my descendants will rule after me, I must eradicate all rebels and antagonists.
Malbim (4): Even though Adoniyahu merely desired her for her beauty, and she did not have the law of a king's widow, Shlomo with his Chachmah understood that Adoniyahu will not be quiet if Shlomo withholds her from him 1 . Even though both Adoniyahu and Avshalom made themselves king in David's lifetime, regarding taking David's women, they were opposites. Avshalom raped David's concubines in order to show that he despises his father. Adoniyahu desired the one who lied in his father's lap due to lust, and wanted to become king in a way that will not upset his father.
I.e. he will seek to rebel in order that he can become king and take her. (PF)