This can be stated in active form. Ezekiel being given understanding and the ability to speak is represented by his mouth being opened. Alternate translation: "I will open your mouth" or "you will know what to say" or "I will cause you to know what to say" (See: [[rc://en/ta/man/jit/figs-activepassive]] and [[rc://en/ta/man/jit/figs-synecdoche]])
Both of these phrases mean that Ezekiel will speak. In the second phrase it is stated in negative form to emphasize that he will speak. (See: [[rc://en/ta/man/jit/figs-litotes]])
Here the word "sign" refers to something that communicates a special warning to those who see it. Yahweh speaks of Ezekiel and his actions as being this warning. See how you translated this metaphor in [Ezekiel 12:6](../12/06.md). Alternate translation: "You will be a warning for them" (See: [[rc://en/ta/man/jit/figs-metaphor]])
When Yahweh says that people will know that he is Yahweh, he is implying that they will know that he is the one true God who has supreme authority and power. See how you translated this in [Ezekiel 6:7](../06/07.md). Alternate translation: "understand that I am Yahweh, the one true God" or "realize that I, Yahweh, have supreme power and authority" (See: [[rc://en/ta/man/jit/figs-explicit]])