Bereishit 46:1 And Israel and all that was his set out and came to Beer Sheba, and he slaughtered sacrifices to the God of his father Isaac.
Midrash Raba: It doesn’t say “to the God of his father Abraham”. Rabbi Yochanan said regarding this that a person is obligated to honor is father more than the obligation to honor his father’s father. The Rama states in his commentary on Yoreh Deah (Section 140) that we see from here that a person is obligated to honor his father’s father, but the obligation to honor is father is greater.
Torah Temimah Colloquial Translation on Note #1:
The above quote is the opinion of the Rama. The Mahari has the opposite opinion: a person is not obligated to honor his father’s father. Many later commentators wrestled with this question and brought proofs for each of the opinions. The Gra, in his commentary on Yoreh Deah writes a new idea on this topic. The Gra states that the grandson is certainly not obligated to honor his mother’s father. The Gra brings a proof from Midrash Bereshit Raba (Section 98) where it states explicitly that the sons of one’s daughters are not referred to as one’s children.
I have doubts, however, whether the Gemora itself agrees with the Midrash Raba on this question. Note that there are many places in the Gemora where it states explicitly that one’s daughters’ children are referred to as one’s children. For example, in the Gemora Yevamoth 66b the Gemora explains the verse in Deuteronomy 33:9 “Nor did he know his children” as referring to his daughter’s children. Another example is in the Gemora Yevamoth 70a where it comments on the verse in Leviticus 22:13 “if the kohen’s daughter has no children…” and states that it is understood that the verse must include “children’s children”. There it is explicitly discussing a daughter’s children. Another example is in the Gemora Kedushin 68b where it discusses the verse in Deuteronomy 6:4 “if he will turn your son from following Me…” and concludes that this includes the children that your daughter may have even with a non-Jewish father. There are many other Gemoras that prove the same point. We additionally see the same with Lavan’s statement in Genesis 31:43 that “the sons are my sons” when speaking about his daughters’ children. Therefore, it seems probable to say that the Gemora disagrees with the Midrash Raba quoted above. The Gemora’s opinion is that the children of one’s daughters are referred to as one’s children. Thus, the view of the Gra would have to be investigated further in terms of its halachic ramifications.
Consequently, in general, it is logical to state that one is obligated to honor one’s father’s father. We see that the father’s father is [himself] obligated equally to the father. As it states in Gemora Kedushin 30a “how do we know that a grandfather is obligated to teach his grandchildren Torah? From the verse in Deuteronomy 4:9 “But beware and watch yourself very well, lest you forget the things that your eyes saw, and lest these things depart from your heart, all the days of your life, and you shall make them known to your children and to your children’s children”.
If so, the logical conclusion is that since the father’s father has the strictness of the obligation regarding educating his grandchildren, similarly the grandchildren have the strictness of the obligation regarding giving him honor.
There is, in actuality, nothing new in this conclusion. We find similar statements by the Rif and the Rosh and other halachic commentators in their comments on the Gemora Kedushin 44a regarding the obligation of a person to make a blessing if a miracle occurs for him. The commentators state that this obligation occurs not only if the miracle happens to the person himself, but also to his children and his children’s children. The reason for this derives from the Midrash Raba’s statement regarding the verse in Genesis 21:23 [And now, swear to me here by God, that you will not lie to me or to my son or to my grandson; according to the kindness that I have done with you, you shall do with me, and with the land wherein you have sojourned.”] The Midrash Raba comments there that father’s have mercy onto their children up to the 3rd generation of descendants. If so, then the reverse is also true that the son and the son of the son have mercy on their father and grandfather. Thus, since according the measure of feelings of the son of the son and the father of the father are the same and we obligate them equally to make a blessing with God’s explicit name, so to it is logical to obligate them to honor [the father’s father].
Editor’s Note: In this note, the Torah Temimah disagrees with the Gra (The Vilna Gaon) and states that it is an obligation to honor one’s father’s father. Additionally, the Torah Temimah digresses slightly to show that the Gemora and the Chumash consider one’s daughter’s children to also be included.