vehineh sulam mutzav artzah - and behold a ladder was set up on the earth
According to the plain meaning of the text (that Yaakov subsequently describing what he had seen and what it meant) Yaakov observed that the feet of the ladder stood in Beer Sheva, where he was lying; this is the meaning of the words mutzav artzah, whereas the meaning of the words, "he top of it reached toward heaven" refers to the Beit HaMikdash (Temple). This is the gateway from which the angels ascend to heaven or descend to earth. When G-d appeared to be standing on top of the ladder, Yaakov realized that the site he was lying on was the gateway to heaven, and that it was an appropriate place for prayer. The Holy Temple is the House of G-d. Yaakov realized that the Holy Temple was of crucial importance in channeling communication from man to G-d and vice versa.
Rashi too quotes Bereishit Rabbah 68, where Rabbi Eleazer in the name of Rabbi Yossi ben Zimra describes the bottom of the ladder as standing at Beer Sheva, the angel being such that the top was vertically above Mount Moriyah. When the Midrash spoke about the angle of elevation, it meant that at its zenith the ladder was above Mount Moriyah. In other words, the point at which it appeared to reach heaven was directly above where the Holy Temple would stand in the future.
The Midrashic approach sees the dream as hyperbole of the revelation at Mount Sinai in the future. The word sulam, ladder, is equated with sinai, Mount Sinai. The numerical value of the letters in both words are the same, i.e. 130. The words mutzav artzah are a reference to the Jewish people who would stand at the bottom of the Mountain at the time of the Revelation.
According to Pirke de Rabbi Eliezer 35, G-d showed Yaakov in his dream the four empires who would host Yisrael in its various exiles, showing them to him in their ascendancy as well as in their eventual decline. He showed him how the celestial representatives of the Kingdom of Bavel (Babylon) would ascend seventy rungs on the ladder only to descend all of them again. He showed him the Medes ascending 52 of the rungs of this ladder and then descending again. Then He showed him that the spiritual representative of the Greek Empire ascended 180 rungs of this ladder only in order to have to descend all of them again. Finally, he showed Yaakov how the spiritual representative of the Roman Empire climbed the whole ladder without descending. While doing so that representative boasted that he would conquer heaven whereas Yaakov quoted Yeshayahu 14:14 where the descent of the Roman Empire is predicted also by the words "but You will bring him down to She'ol." G-d had told him "even if you rise like the eagle I will bring you down from there" (Ovadyah 4)
According to this Midrash Yaakov's dream contained a prophetic message that at the end of all the various exiles the Jewish people would resume their leading role in the world, seeing that all the patriarchs had similar visions starting with the covenant between the pieces when Avraham was first told about the exile his descendants would experience before they would inherit the land of Yisrael as their homeland. (various Midrashim concerning Bereishit 15:12).
Other Midrashim variously describe the angels Yaakov saw ascending and descending as the angels of Sedom which had been demoted as their charges had been destroyed, or that they were the angels who accompanied Yaakov while he was in Eretz Yisrael now taking their leave in order to be replaced by other angels who would guard him while he was in Charan, etc.
Other Midrashim describe the angels Yaakov saw ascending and descending as inquisitive angels who wanted to get a close up look at the choicest of the patriarchs, Yaakov, whose likeness was engraved on G-d's throne. None of these Midrashim are mutually exclusive as the ladder was not narrow and may angels were able to climb or descend at the same time, each one at his own speed.
A rational approach to the dream is that the ladder represents the various levels of this universe. The universe may be regarded like a pyramid with the terrestrial part, the part inhabited by man at the bottom of the pyramid. Above our world is that of the planetary system; still "higher" is the world inhabited by disembodied creatures. In other words, the ladder has three basic rungs. David also characterized the world in a similar manner when he said, "bless Hashem, His angels" (Tehillim 103:20) He followed this by saying, "bless Hashem, all His hosts, His servants, who do His will." (v21) Finally, he said, "bless Hashem all His creatures..." (v22).