Jamieson, Fausset and Brown on Ezekiel 9:6

6. come not near any ... upon whom ... mark--(Re 9:4). It may be objected that Daniel, Jeremiah, and others were carried away, whereas many of the vilest were left in the land. But God does not promise believers exemption from all suffering, but only from what will prove really and lastingly hurtful to them. His sparing the ungodly turns to their destruction and leaves them without excuse [Calvin]. However, the prophecy waits a fuller and final fulfilment, for Re 7:3-8, in ages long after Babylon, foretells, as still future, the same sealing of a remnant (one hundred forty-four thousand) of Israel previous to the final outpouring of wrath on the rest of the nation; the correspondence is exact; the same pouring of fire from the altar follows the marking of the remnant in both (compare Re 8:5, with Eze 10:2). So Zec 13:9; 14:2, distinguish the remnant from the rest of Israel.

begin at ... sanctuary--For in it the greatest abominations had been committed; it had lost the reality of consecration by the blood of victims sacrificed to idols; it must, therefore, lose its semblance by the dead bodies of the slain idolaters (Eze 9:7). God's heaviest wrath falls on those who have sinned against the highest privileges; these are made to feel it first (1Pe 4:17, 18). He hates sin most in those nearest to Him; for example, the priests, &c.

ancient men--the seventy elders.