Thus Ezekiel is unto you a sign: according to all that he hath done shall ye do: and when this cometh, ye shall know that I am the Lord GOD.
Thus Ezekiel is unto you a sign - a typical representative, in his own person, of what was to befall them (so Isaiah 20:3).
And when this cometh - alluding probably to their taunt, as if God's word spoken by His prophets would never come to pass: "Where is the word of the Lord? Let it come now" (Jeremiah 17:15).
Ye shall know that I am the Lord God. When the prophecy is fulfilled, "ye shall know (to your cost) that I am the Lord," who thereby show my power and fulfill my word spoken by my prophet (John 13:19; John 14:29).