Why is he called a Mevaser? He had bad tidings!
Radak: 'Mevaser' applies to good or bad news.
Kli Yakar: This is like Chazal expounded why it says "Mizmor l'Asaf" and not Kinah l'Asaf. A parable for this is a poor woman who dropped a Kli in s pit, and cried. A princess came and dropped a gold Kli there. The Aniyah rejoiced, for they will retrieve the gold Kli, and her Kli with it. 2 Here, Hashem will avenge the capture of the Aron, and avenge also the Yisraelim killed.
Malbim: Mevaser tells what the listener wants to hear. He assumed that Eli already knew, and wanted to hear details.
Rav Elyashiv (Pesachim 3b, citing Imrei Noam Brachos 54a): We say 'Besoros Tovos', for it is permitted and a Mitzvah to say good tidings openly and explicitly. We say "Shemu'os Ra'os", for they are said only via hints; the listener understands by himself. (Why did he have earth on his face, and his clothes were torn? Perhaps he showed that even though he retrieved the Luchos, he still mourns the capture of the Aron. - PF)
Tosfos (Kidushin 31b) brings this with a minor change.
Why did he tell him suddenly about the death of Bnei Eli and the Aron's capture, which caused Eli's death? "One who says bad words is a fool" (Mishlei 10:18)!
Malbim (14): Eli heard the tumult in the city, and asked about it. No one wanted to tell him the bad news 1 . The herald rushed to tell him. He assumed that Eli had heard the gist of what happened, and he wanted to hear details. He rushed, and told everything suddenly.
The Meforshim on Mishlei 10:18, including Malbim, explain Dibah to be Leshon ha'Ra. However, Pesachim 3b implies that it includes bad tidings. (PF)
Why does it say "Nilkechah" (feminine)?
Midrash Shmuel 11:2: Midas ha'Din became weak like a female. 1
Radak: 'Aron' is usually masculine, e.g. "v'Aron ha'Elokim Nilkach" (verse 10). Here it is feminine, and also "Ba'ah Aleihem Aron Hashem" (Divrei ha'Yamim 2 8:11).
Presumably, this is like Eichah Rabah 4:14. Tehilim 79 is called "Mizmor l'Asaf" and not Kinah l'Asaf, for Hashem vented his anger on the Mikdash, and not on Bnei Yisrael. Here, after the Aron was taken, Midas ha'Din could not claim that Yisrael deserve any more punishment. (PF)