Adam Clarke on Genesis 28:17

How dreadful is this place! - The appearance of the ladder, the angels, and the Divine glory at the top of the ladder, must have left deep, solemn, and even awful impressions on the mind of Jacob; and hence the exclamation in the text, How dreadful is this place! This is none other but the house of God - The Chaldee gives this place a curious turn: "This is not a common place, but a place in which God delights; and opposite to this place is the gate of heaven." Onkelos seems to suppose that the gate or entrance into heaven was actually above this spot, and that when the angels of God descended to earth, they came through that opening into this place, and returned by the same way. And it really appears that Jacob himself had a similar notion.