Hashem Promises Gavriel, Yidden Will Always Be Moser Nefesh
Here is a Dvar Torah I once heard from R' Elya Svei, ZT"L, about a posuk in Hallel. The gemara in Arvei Pesachim says that the posuk of "V'Emes Hashem L'Olam Haliluka" was said by Gavriel. When Avraham Avinu was thrown into the Kivshan HaEish, Gavriel wanted to save him. Hashem said that it was proper for Hashem himself to save Avrohom, but he'll pay back Gavriel with a different chance to save someone from fire. Gavriel was allowed to save Chanaya, Mishael, V'Azariah from the fire many years later. At that point, Gavriel said "Vemes Hashem L'Olam "
Reb Elya asked, didn't Gavriel know that Hashem is truthful and keeps his promises before then? What did he find out new? Reb Elya answered that Gavriel wasn't sure if there would be more people who would be moser nefesh for Hashem like Avraham did. When he saw Chanaya, Mishael, V'Azariah , he saw that Hashem would make sure that there would always be people in Klal Yisrael that would be ready to be moser nefesh for the Ribono Shel Oilem. That was the "truthfulness" that he found, truthful to keep the midah of mesiras nefesh in Klal Yisrael. (R' Abba Moshe Barer)