Genesis 28:17

And he was afraid, and said, How dreadful and glorious is this place! This place is not common, but the sanctuary of the Name of the Lord, the proper spot for prayer, set forth before the gate of heaven and founded beneath the throne of glory.

THIS IS NONE OTHER THAN THE HOUSE OF G-D, AND THIS IS THE GATE OF HEAVEN. This refers to the Sanctuary which is the gate through which the prayers and sacrifices ascend to heaven.
Rashi comments, Rabbi Elazar the son of Rabbi Yosei the son of Zimra said, ‘This ladder stood in Beer-sheba and its slope reached unto the Sanctuary in Jerusalem. Beer-sheba is situated in the southern part of Judah, and Jerusalem is to its north on the boundary between Judah and Benjamin, and Beth-el was in the northern portion of Benjamin’s territory, on the boundary between Benjamin’s territory and that of the children of Joseph. It follows, therefore, that a ladder whose base is in Beer-sheba and whose top is in Beth-el has its slope reaching opposite Jerusalem. Now regarding the statement of our Rabbis that the Holy One, blessed be He, said, ‘This righteous man has come to the place where I dwell, [namely, the Sanctuary in Jerusalem, and shall he depart without spending the night?’], and with regard to what they also said, ‘Jacob gave the name Beth-el to Jerusalem’ this place which he called Beth-el was Luz and not Jerusalem! And whence did they learn to say so, [implying that Luz is identical with Jerusalem]? I therefore say that Mount Moriah [the Temple site in Jerusalem] was forcibly removed from its place and came here to Luz, and this movement of the Temple site is ‘the springing of the earth’ which is mentioned in Tractate Shechitath Chullin. It means that the site on which the Sanctuary was later to stand came towards Jacob to Beth-el. And this too is what is meant by vayiphga bamakom (and he met the place): [as two people meet, who are moving towards each other]. If you should ask, ‘When our father Jacob passed the site of the Sanctuary [on his way from Beer-sheba to Haran] why did He not detain him there?’ The answer is: If it never entered his mind to pray at the place where his fathers had prayed, should Heaven make him stop there? He had journeyed as far as Haran, as we say in the chapter of Gid Hanasheh, and Scripture itself helps us clarify this point by saying, And he went to Haran. When he arrived at Haran he said, ‘Is it possible that I have passed the place where my fathers prayed without praying there myself?’ He decided to return and had returned as far as Beth-el, whereupon the ground of the Temple site sprang for him until Beth-el.”
All these are the words of the Rabbi.. But I do not agree with them at all for ‘the …

ויירא, about the error he had committed in lying down there.

אין זה, this place I saw in my dream that the ladder was standing upon. It can be none other than בית אלוקים, the site of the Temple. Our sages (Pessachim 88) have said that Yaakov called the Temple “house,”

וזה שער השמים, and this ladder which I have seen in my dream that G’d stood upon is the gate to heaven. Mankind’s prayers must be viewed as ascending to heaven by means of this ladder, as we quoted earlier from Chronicles ותעל שועתם למעון קדשו השמים, “their prayer rose to the residence of His Holiness, to heaven.”

ויירא ויאמר, he was concerned for himself fearing that he might have done something which one is not allowed to do in a holy place. Perhaps while he had been asleep and unable to control his movements, he had behaved in a manner unbefitting such a sacred location.

ויאמר מה נורא המקום הזה, since he had seen an awe-inspiring vision here he concluded that the whole place may have been an awesome place, not to be approached except in a state of ritual purity.

אין זה כי אם בית אלוקים, this place is suitable only for becoming a House of G’d, a temple of sorts. a place wherein to pray and to offer sacrifices to G’d. Another explanation of Yaakov’s exclamation could be that he concluded that the only reason he had been shown the vision was to stimulate him to erect a House of G’d there.

וזה שער השמים, an expression analogous to Chronicles II 30,27 ותבא תפלתם למעון קדשו לשמים, “their prayer reached the residence of His Holiness, to heaven.”

אין זה כי אם בית אלהים. “this must surely be the house of G–d.” Seeing that I observe the angels first ascending and then descending and then remaining down on earth this spot on earth and the region in the heavens above must belong to one entity. The angels ascend within this “house” and descend, just as human beings ascend to the upper floors in their houses when the occasion demands it, and then come down again remaining there.