The one where the Lord appoints Ezekiel as watchman for the house of Israel – Ezekiel 3:16-21
Now it came to pass at the end of seven days that the word of the Lord came to me, saying, “Son of man, I have made you a watchman for the house of Israel; therefore hear a word from My mouth, and give them warning from Me: When I say to the wicked, ‘You shall surely die,’ and you give him no warning, nor speak to warn the wicked from his wicked way, to save his life, that same wicked man shall die in his iniquity; but his blood I will require at your hand. Yet, if you warn the wicked, and he does not turn from his wickedness, nor from his wicked way, he shall die in his iniquity; but you have delivered your soul.
“Again, when a righteous man turns from his righteousness and commits iniquity, and I lay a stumbling block before him, he shall die; because you did not give him warning, he shall die in his sin, and his righteousness which he has done shall not be remembered; but his blood I will require at your hand. Nevertheless if you warn the righteous man that the righteous should not sin, and he does not sin, he shall surely live because he took warning; also you will have delivered your soul.”