Shabbos 32b, Rashi: Even if one angel advocates, amidst 1000 that tell his sin [he will be saved - "Peda'ehu" (24).] Some say, even if the advocate has 999 reasons to condemn, and one reason to acquit, he will be saved - "Melitz Echad Mini Elef."

Ibn Ezra: The angels that kill and seek a man's Nefesh are many; one angel is appointed over him to guard him. One who understands the arrangement of legions will admit to this.

Malbim: There are three ways to be saved from death. (a) Merits - if he did a Mitzvah worthy to save him. The merit is called Mal'ach. It goes on Shelichus to advocate for him. Even if Hashem sent thousands of opportunities for him to do Mitzvos, and he fulfilled only one of them, it will advocate for him. Also refer to 33:26:3:1, 33:27:1:3.

Ibn Ezra: He tells on behalf of man. Also "Imri Li Achi Hu" (means 'say on behalf of me').