How does "ancestral merit" work?

Question

We see the usage of Zechut Avot, which I loosely translate as "ancestral merit" used in numerous circumstances to ask God to forgive our sins and wrongdoings. Moses used this several times such as forgiveness for the sin of the Golden Calf, when Israel complained about lack of meat and several other places.

We refer to this merit in various places in our prayers such as during Tachanun and Selcihot.

When does this work and when doesn't it? For example, Moses didn't refer to this after the sin of the spies. Ancestral merit didn't seem to ward off the Destruction of the Temples.

Does ancestral merit work only for certain types of sins? Is there some type of "expiration"? For example, is there a limit for how many sins or a frequency for which we can ask God to forgive us for such sins, but if we are "too sinful" this no longer works? Is ancestral merit meant to be a "supplement" for teshuva (repentance) or in what way is it meant to be used?

Answer 1

Generally speaking, zechus avos seems to work in 2 ways.

1. Behavioral: By inheriting the zakus (purity of character) of the avos, we are more inclined to align ourselves with the ratzon Hashem in the long term, even if we have fallen short currently. One of the primary sources for this notion is in the Nephesh Hachayim, where Rb Chaim Volozhin discusses why in the following mishna

https://he.wikisource.org/wiki/%D7%9E%D7%A9%D7%A0%D7%94_%D7%90%D7%91%D7%95%D7%AA_%D7%94_%D7%91

עשרה דורות מנח ועד אברהם

Avraham is just referred to by name, whereas in the following mishna

https://he.wikisource.org/wiki/%D7%9E%D7%A9%D7%A0%D7%94_%D7%90%D7%91%D7%95%D7%AA_%D7%94_%D7%92

עשרה נסיונות נתנסה אברהם אבינו

Avraham is referred to as "avinu". He answers that by passing the 10 tests, Avraham bequeathed to us the purity of character to do the same, and in this regard he is "avinu".

2. Hashem's plan for the world: Hashem made a bris with the avos that they are their descendants would be central to Hashem's plan for the world. By invoking zechus avos we reconfirm our commitment to be part of that plan, and thereby request that Hashem should have mercy on us, despite our shortcomings, so we can continue to implement His plan for the world's destiny; in other words, to be mekadesh shem shamayim. This is a frequent theme in the tefillos of the yamim noraim, for example: Zachreinu le'chayim le'maanchah Elokim chayim.

Apparently we should say tamah zechus avos when neither of the above 2 mechanisms can be invoked.

Answer 2

Rav Eliyahu Dessler in Michtav M'Eliyahu (cheilek alef - p.8) has an essay that focuses on understanding G-d's trait of Rachamim - mercy, and in particular, how it manifests itself along with Zechus Avos.

He focuses on the specific middos that the avos excelled in and notes how it is this that creates a link to future generations. Their devotion and mesirus nefesh to the cause is what creates is our innate, ancestral link. For this reason one should read it not as 'zechus' but rather 'zakus' meaning the purity of the avos.

He writes on p.15:

הלא הבטיח השי"ת לאבות הקדושים כי תכלית כל הבריאה כולה תצא מהם וזרעם, וכל העתיד הגדול אשר יתגדל ויתקדש שמו של הקב"ה לעין כל, הלא יהיה על ידי משיח צדקינו. אבל הלא מאברהם אבינו ע"ה על דורו של משיח ישנן דורות הרבה, וכולם יוצאים אלו מאלו כמו השלשלת הארוכה, אשר טבעותיה דבוקות זו בזו. ובאופן כזה יש דורות או יחידים, שעל פי משפט מעשיהם אינם ראוים להתקיים, אבל מ"מ מתקיימים, לא בזכות עצמם אלא בזכות אבותיהם וצאצאיהם. כי הדור הזה, או האנשים הללו, המה כמו טבעת בשלשלת החבור ההיא, ובזה היא סבת קיומם, כי בלעדיהם אין חבור בין אבותיהם לדורות יבואו. אדם אשר כזה יתקיים בעולם הזה, אף שאין לו שום זכות לזה מצד עצמו

Did Hashem not promise to our holy forefathers that the purpose of all creation will come out of them and their seed, and all the great future which will grow and be sanctified in His name Hashem will be for all to see, and will it not be through Moshiach. But aren't there many generations from the point of Avraham avinu? All of them (i.e. the generations) come out of each other like a long chain whose rings are all linked with each other. And in this way there are generations or individuals, which according to the law of their deeds are not worthy of existence, but nevertheless they exist, not due to their own merits but the merits of their forefathers and their descendants. Because this generation, or these people, they are like rings in a chain that are interconnected, and this is the reason for their existence. Because without them, there would be no connection to the generations to come. A person like this will exist in this world, even though he has no right to it on his own part.

So to answer your question it would seem from Rav Dessler that this ancestral merit serves to aid our continued existence even when we are deemed unworthy. They showed us the correct way to act and these traits are something that we as a nation have been gifted throughout the generations.

Answer 3

The concept of zechut avot, “merits of the fathers" is problematic because it implies that the individual’s merit can be stored in a bank account and be used at a later date. The idea is linked to the flawed Christian notion called “original sin,” which some attribute to Genesis 1. Both ideas are contrary to the Torah. Thus, zechut avot "ancestor’s good deeds" is not a biblical concept at all. It follows that it does not [and cannot] work. How then, could Moses used his merit to save the Israelites?