Or HaChaim on Genesis 28:17/אור החיים על בראשית כ״ח:י״ז

1"Shaken, he said..." He felt that his heart was moved to fear on its own, and gave a reason for this when he said "this is none other than the abode of God." He was careful to use the Divine name Elohim, because this is the source of fear, as it is written "...and God (Elohim) made it so that they fear Him." (Kohelet 3:14) It is known that the name Elohim strikes fear in the heart of man.

2When Yaakov said "this is the gate..." he meant that the place aligned with it above is the gate of heaven. This is why he used the word 'this' (zeh) twice.

3He also intended to explain the lofty status of the place by saying that this is the House of God, a physical place preceded by the knowledge that God had chosen a place to cause His name to dwell. He said 'this is that place!' He proved further that this was the chosen place when he said 'this is the gate of heaven.' Yaakov said this because he saw angels rising and descending, and he already knew that the sacred place below was aligned with the gate of heaven: