Dear Rabbi Kornfeld:
On the subject of z'chus avos (daf 55a) the gemara seems to conclude that z'chus avos has bee "used up" long ago, and now, z'chus avos dependson G-d's mercy. What about our "plea" in the 13 middos..."notzair chesed l'alafim"? I always understood that to mean that G-d's chesed directed toward b'nei yisrael is on account of z'chus avos, and lasts for 1,000 generations! And we're asking G-d to be merciful on us in "z'chus avos". It also seems that if we would want to say that this too depends on G-d's mercy, and we're asking him to be merciful and use z'chus avos in judging us, why is the "plea" formulated the way it is...that is, why doesn't the request mention "a time of mercy". Additionally, it also seems that we're invoking z'chus avos during the 1-st b'racha of Shemona Esray as well. If z'chus avos depends on G-d's mercy, why wasn't the prayer formulated with that idea apparant?
as always, warm regards,
"Notzer Chesed la'Alafim" refers to the Zechuyos created by your own Mitzvah-observance, which endures for thousands of generations --for your own descendants, as Rashi on the verse (Shemos 34:7) explains. It is not related to Zechus Avos. The Zechuyos which protects a person's descendants for thousands of generations are not as potent, so to speak, as Zechus Avos. Zechus Avos protects the Jewish people even when they are not going in to the ways of their forefathers; nevertheless, Hash-m still protects them from annihilation due to their Zechus Avos. One's own personal Zechuyos can only help one's descendants in arousing Divine mercy for them, but will not serve to save them from destruction if they deserve it, G-d forbid, because the Zechuyos of their fathers only helps them when they follow in the ways of their fathers (as the Gemara in Berachos 7a states).
Concerning invoking Zechus Avos in the first Berachah of Shemoneh Esreh (as we wrote in Insights to Berachos 7b, #2), see the Insights here, where we offer several resolutions.