God judges and kills all idolators and any not grieved over the idolatry, starting with the elders at the gate. As at Passover in Egypt, He spares those who look to the Lord by giving them a mark.
God's glory goes to the eastern gate of the temple. There is more emphasis here on the cherubim than on God's presence, implying they are closely connected. Perhaps we are also supposed to recall the exile from Eden, when the cherubim were stationed at the east gate, just like here.
Israel's leaders feared the sword, so they would fall by it, just as Caiaphas acted out of fear of the Roman sword, seeking to keep his place and nation. Israel fell both times, and it will continue to happen every time God's people fear worldly governments more than Him. God speaks once more that the land will be removed of wicked men. But wherever the faithful are scattered, God will be a sanctuary to them there (a portable temple, as we've seen in the cherubim visions). And He will bring them back, with a new heart and spirit. With this word of judgment and promise, God leaves, to the east, landing first on a mountain east of the city (Mt. Olive?).
Ezekiel acts out the coming exile, in front of an apathetic people who think it is a long way off.