What is the significance of the ladder? Why were the angels first ascending and then descending?
Rashi and Ramban #1: Yakov was about to leave Eretz Yisrael on his way to Charan. 1 So in his dream, he saw the 'changing of the guards' - the angels of Eretz Yisrael that had accompanied up to the border of Eretz Yisrael returning to their place in Heaven 2 and the angels of Chutz la'Aretz 3 that were waiting to accompany him till he arrived in Charan.
Targum Yonasan: The angels who had accompanied him until now were the same angels that had gone to S'dom and that, having sinned by revealing Hashem's secret (that He was about to overturn S'dom) to Lot, were denied permission to return to Heaven - until now. So he saw those angels ascend to Heaven, whereas the angels who were descending the ladder were coming to look at him. 4
Rashbam: The angels were going up and down the ladder. The order is not significant, since it is obvious that they descended first. 5
Ramban #2: Hashem showed Yakov that (a) everything that He does in this world is via angels, and (b) that the angels do not act independently, but by the command of Hashem. 6
Ramban #3: He also showed him how He was standing on top of the ladder watching over him, and He assured him that he (Yakov) would never under the jurisdiction of the angels, but directly under His personal jurisdiction (Hashgachah P'ratis). 7
Ramban (citing Pirkei d'R. Eliezer), Da'as Zekenim #2: Like the Bris bein ha'Besarim (in Lech Lecha), this was a prophetic vision concerning the four exiles 8 , at the hand of Bavel, Medes, Greece and Edom. 9
Da'as Zekenim #1, Hadar Zekenim: The ladder represents Har Sinai. The angels are Moshe and Aharon.
Tosfos ha'Shalem (6, and 20:4, citing R. Efrayim): The ladder shows that man is a microcosm of the world. His roots are in Shamayim, unlike trees. The ladder hints to three intellects (Nefashos) in man - the lowest is the source of physical lusts, the intermediate is the source of pride, anger and Ratzon, and the highest is spiritual, and aspires to Chachmah. The angels hint to Neshamos, which ascend (are drawn to the higher Sechel) or descend (towards Gashmiyus).
Ba'al ha'Turim, from the Zohar: The voice of prayer of Tzadikim is the ladder of angels. If one has intent in his prayer, the angels can ascend on it.
Tosfos ha'Shalem (11) citing Bereishis Rabah 68:12: "Artzah" hints to the Mizbe'ach; the ladder is the ramp, the smell of the Korbanos ascends to Shamayim, and the Kohanim go up and down.
Ha'Emek Davar: This hinted that the Shechinah is below on the land, surrounded by angels. This is a sign that Hashgachah Pratis will surround Yakov.
Ha'Emek Davar (13): The angels represent angels of other nations. Yakov is the foundation of Yisrael's exiles. He went to Charan, returned to Eretz Yisrael, and was exiled against to Egypt. So Yisrael went to Bavel, returned, and were exiled again.
Malbim (17): Through Tefilos and Korbanos brought here (in the Mikdash), angels ascend, and bring down an influence of abundance.
Moshav Zekenim, Tosfs ha'Shalem (7) citing R. Yakov of Vienna citing Ri of Orleans: He already went to Charan, and the angels of Eretz Yisrael departed! When he returned to pray, they returned.
Hadar Zekenim (verse 13): Angels who gave their wings to a girl (who refused their enticement, and she flew to Shamayim and became Mazel Besulah) were unable to return to Heaven until now. Alternatively, they were the angels sent to destroy Sedom.
Tosfos ha'Shalem (2, citing R. Efrayim): The two angels that accompany a person during the day ascend to record his actions that day, and two descend to guard him at night.
Because the former told them that Yakov, whose image is engraved on the Divine Throne, and whom they were eager to see in person, was actually right there at the foot of the ladder, so they were coming to see him in person.
The Rashbam does not indicate who the angels were. See Ba'al ha'Turim, who presents a variety of explanations.
As the angels who had accompanied him until now returned to the Heaven to report to Hashem what they had done and what the situation was.
Since he was a cut above other Tzadikim, about whom the Pasuk writes in Tehilim (91:11) "For He commands His angels to guard you wherever you go".
Pane'ach Raza: Hashem showed him that the angels ascend and descend with the Shechinah, which is with Yisrael in exile.
He showed him how the angel of Bavel climbed 70 rungs before descending, the angel of Medes, 52 rungs, the angel of Greece, 180 rungs, corresponding to the number of years that these nations would enslave his children. Then he saw the angel of Edom climbing and climbing and climbing. In response to his prayers, Hashem citing the Pasuk in Ovadyah (1:4), assured him that, "Even if you (Edom) will raise your nest like an eagle, from there will I bring you down!"
How wide was the ladder?
Chulin, 91b: It was eight thousand Parsah (ytwo thousand Mil) wide; since "Olim ve'Yordim bo" implies that there were four angels on the ladder simultaneously, two climbing up and two climbiing down - and each angel is the width ot the Sea of Tarshish, which was two thousand Amos wide (See Gemara there).
Why is "Hinei" repeated in the dream?
Ohr ha'Chayim: Normally, dreams are imaginary, and the matters are not perceived clearly. Here, everything was with utter clarity