Shemini Atzeret is such a confusing holiday. Is it part of Sukkot, or isn’t it? Why the confusion? In one place in the Torah, Sukkot is seven days long (Deut. 16:13-15). Similarly, the mitzvah of lulav and etrog and that of dwelling in the Sukkah are commanded explicitly for seven days. (Leviticus 23:34,42) Elsewhere, though, the Torah speaks of the eighth day of Sukkot as “Atzeret – the Assembly”. (Leviticus 23:35-6). And in another place, it is called the “eighth day” but is marked off as distinctive. (Numbers 29:35)
One midrash noted a profound message in the difference between these two closely linked holidays. During the duration of Sukkot, seventy bull were offered as sacrifices while on Shemini Atzeret, only a single bull was offered. This sacrificial distinctive led to the following parable: “Rabbi Alexandri told the parable of a king to whom an occasion for rejoicing came. Throughout the seven days of feasting, the king’s son was busy with the guests. But after the seven days of feasting had run their course, the king said to his son: My son, I know that throughout the seven days of feasting you were burdened with the guests, but now let you and me rejoice for one day, and I shall not burden you further except to require from you one cock and one pound of meat. So, too, throughout the seven days of feasting Israel are occupied with offerings for the nations of the world. As Rabbi Phinehas said: All those seventy bullocks which Israel offer during Sukkot are on behalf of the earth’s seventy nations. After Sukkot’s seven days had run their course, the Holy One said to Israel: My children, I know that throughout Sukkot’s seven days you were engaged with offerings for the earth’s nations. Now let you and Me rejoice together, and I shall not burden you much except for requiring you to offer Me one bullock and one ram. When Israel heard God speak thus, they began to praise the Holy One, saying This is the day which the Lord has made; we will rejoice and be glad (Ps. 118:24).” (adapted from Pesikta deRav Kahana 28:9 Mandelbaum ed. p. 432)
The takeaway from this midrash is that Sukkot and Shemini Atzeret are one that are two or two that are one. On Sukkot, the children of Israel show their universal concern for the nations of the world. It is a holiday for all of humanity and teaches Jews that God is concerned with the entire world. That said, Shemini Atzeret is a reminder that the Jews are nothing is they do not maintain their own identities as Jews and nourish it. For a true Jew, these two visions are not at odds with each other. They are complementary, just as Shemini Atzeret is integral to Sukkot.