Would you please explain to me the notion of ancestors’ merit benefitting or affecting a person? How does this work and in what ways is it expressed?
The notion you refer to is called zechut avot in Hebrew, or the merit of one’s forebearers. It describes the general or particular good influence over a person resulting from the good deeds, righteousness, and piety of one’s ancestors. It can be expressed in the form of protection from harm, Divine aid, beneficial opportunities or even as a pre-disposition for righteousness.
You can think of it as a type of “spiritual inheritance” from one’s predecessors, which bequeaths certain advantages according to the nature and extent of the inheritance.
For example, someone whose ancestors were tall will very likely inherit the innate advantages of being tall. This is so even though the person himself did nothing to “deserve” these advantages. Nevertheless, they will nevertheless accompany him throughout life.
Similarly, internal traits (such as a pleasant temperament), or talents (such as musical ability), may also be passed down from forebearers to progeny. These beneficial traits and talents become part of the matrix in which the person operates and with which he experiences life.
So too with ancestral merit. The good deeds, Torah study, and piety accrued by the righteous are passed to and continue to have a beneficial effect on, their descendants. This is the case even if the descendants don’t deserve it in their own right. In which case, it will likely accompany them generally or particularly throughout life until it is depleted. But hopefully, this ancestral merit will provide the opportunities and pre-disposition upon which the offspring can capitalize in order to continue the righteous ways of their forebearers.
We find this idea in the resolution of seemingly contradictory Talmudic teachings regarding in whose merit the Jews received the miraculous manna, clouds of glory and traveling well of water.
According to one Talmudic source, they were given in the merit of Avraham’s hospitality to the angels (Gen. 18:4). The teaching thus states (Bava Metzia 86b): “As a reward for the ‘milk and butter’ [which Avraham served to his visitors], they received the manna; as a reward for ‘and he stood over them [to serve them]’, they received the pillar of the cloud; as a reward for ‘let some water be taken [to wash their feet], they received the well of Miriam”.
However, the Maharsha notes a contradictory Talmudic source (Ta’anit 9a) which attributes the manna, clouds of glory and well of water to the merit of Moshe, Aharon and Miriam, respectively.
So the question is, were these miracles performed for the Jewish People in the merit of Avraham or rather in the merit of Moshe, Aharon, and Miriam?
The answer is that the gifts were bestowed as a result of a process, not due to a single event or individual. The process began with the righteousness of Avraham, whose merit planted the seed of possibility for the miracle to occur. This ancestral merit of Avraham was passed on in potential to his progeny – Moshe, Aharon, and Miriam. They then capitalized upon their ancestral pre-disposition for righteousness and brought that seed of merit into fruition through the formation of the manna, clouds of glory and the traveling well.