1)
How was Avner getting stronger?
1.
Rashi: He was getting stronger within Beis Sha'ul to establish [Ish Boshes'] kingship.
2.
Malbim: Initially the kingship was attributed to Ish Boshes. After the war [between Beis Sha'ul and Beis David], since he was not a warrior - this is why we do not find him with Sha'ul in the war against Pelishtim - Avner, the head general, was fighting and reigning. He became stronger in Beis Sha'ul. He ran the house and the kingship. We see that he was brazen towards his king without fear (verse 8)!
