Q. Does Ezekiel 33:1-9 mean we are to speak up when we see wicked things and warn or hold accountable the person involved in such things, or we will answer for their death? So if we remain silent, this is a sin?
A. Ezekiel 33:1-9 tells of the Lord appointing Ezekiel to be a watchman over Israel, which at the time consisted only of the Southern Kingdom. (This confirmed His earlier statement to that effect in Ezekiel 3:17). Before him, God had said the prophets He sent to the Northern kingdom were watchmen along with Him (Hosea 9:8).
These are the only two places where God speaks of appointing a watchman to warn the people of the consequences of their sinfulness, and both are in the Old Testament and were intended for Israel. And only Ezekiel was held personally accountable for conveying the warning.
There is only one mention of a watchman in the New Testament (John 10:3) and then only in a few English translations. The KJV calls him a porter. Most translations use gate-keeper or door keeper. His job was to open the gate of the sheep pen so the shepherd could retrieve his sheep.
A porter is also mentioned in Mark 13:34. Here the Lord was telling believers who will be on Earth at the time of the Second Coming to be on guard and be alert, like a porter stands at the door and awaits His master’s return. The door keeper/porter was not commanded to warn the people of their sins in either of these cases.
In summary, I believe Ezekiel 33:7-9 was intended specifically for Ezekiel and was not meant to have application in the Church today.