“The children of one’s children are considered as one’s children.”
This statement, made by the gemara on our daf, helps explain a halacha regarding the daughter of a kohen being permitted to eat teruma. Before marriage to a non-kohen, she may eat teruma. However, if she marries a non-kohen, she may not. But if she is widowed or divorced and does not have children, she may once again eat teruma, as the verse states, “But if the kohen's daughter becomes widowed or divorced, and she has no offspring (“zera”), she may return to her father's household as in her youth, and eat of her father's food (teruma)....” (Vayikra 22:13). Based on the above principle that her grandchild is like her child, then if she had a son who died, but her son had a son who is alive, she is considered as having a child and may not return to eating teruma. (Rashi)
Rashi explains that this rule of one’s grandchildren being considered as one’s children is derived in another sugyah (Yevamot 62b). The gemara there cites verses in Nach (Prophets and Writings), showing that a specific grandchild mentioned by name, is in fact called “the child” of that person.
Without taking away from this proof, the fact that the gemara proves this idea in the way that it does instead of citing other numerous possible verses in Chumash as the source for this same idea — such as when Hashem promised Avram, “And I will make your seed like the dust of the earth, so that if a man will be able to count the dust of the earth, so will your seed (zaracha) be counted. (Ber. 13:16)” — is seen as puzzling by at least one Torah commentary. (Rashash)
Kiddushin 4a
