When the angels disguised as men went to visit Avraham, he was more than happy to host them. In Breisheet 18:4 Avraham tells his guests: “Let a bit of water be brought and wash your feet. Rest yourselves under the tree.”
In Breisheet Raba 48:10 we learn that Avraham seated the guests under the tree so that they would have a comfortable, protected, shaded place to sit. The Midrash teaches that since Avraham seated them under the tree, his reward would be that his future offspring, B’nei Yisrael would always be protected by God.
When B’nai Yisrael left Egypt, God gave them shade in the desert, as it says in Tehillim 105:39: “He spread out a cloud for shelter, and a fire to illuminate the night.”
How do we know that God also gave Avraham’s offspring shade when they were living in the Land of Israel? In Vayikra 23:42-43 we read: “You shall dwell in sukkot for a seven day period; every native in Israel shall dwell in sukkot so that your generations will know that I caused B’nai Yisrael to dwell in sukkot when I took them out of the land of Egypt.” The sukkah is like a chuppah (canopy) of honor which protects us and gives us shade from all harm, so that in every generation we will remember that God protected B’nai Yisrael and enveloped them in the clouds of glory.
From where do we see that God will protect us and envelope us in the future/ the days of the mashiach (messiah)? Yishayahu 4:6 states: “And there will be a sukkah as a shade from the heat in daytime as a protection and refuge from storm and from rain.”
Since Avraham went out of his way to protect his visitors, the Jewish people will forever be protected by God. It is not a coincidence that the first of the Ushpizin (virtual guests) is Avraham followed by his son, Yitzchak, his grandson, Yaakov, his great grandson, Yosef and his future descendants Moshe, Aharon and David.