God explained to the prophet Ezekiel that genuine prophets are like watchmen who warn of danger, while false prophets are like watchmen who do not warn the people of an impending threat.
1 Again the word of the Lord came unto me, saying
2 Son of man, speak to the children of thy people and say unto them, When I bring the sword upon a land, if the people of the land take a man of their coasts, and set him for their watchman:
3 If when he seeth the sword come upon the land, he blow the trumpet and warn the people;
4 Then whosoever heareth the sound of the trumpet, and taketh not warning, if the sword come and take him away, his blood shall be upon his own head...
5...But he that taketh warning shall deliver his soul.
See, God is using several analogies that people of those times would have well understood. God compares his righteous wrath-God's punishment of humans for sin and disobedience-to a sword bearing raider.
This would have resonated to those times where people lived in great danger of raids and attacks, especially from along the sea and coastline. So the people would have understood that God's wrath can come very quickly and without warning.
However, because God is fair and perfect in his justice, God sends legitimate prophets to warn the people of their sin. So the second analogy is that a prophet such as Ezekiel is like a night watchman who is alert and on guard while the people are asleep.
This would also have resonated with people of Biblical times, as people then could not sleep with the security that many take for granted today. A gated city with a trusted watchman was a great comfort and indeed a necessity. So a prophet like Ezekiel who warns exactly what God is wrathful about and will righteously punish transgressors allows people who are just to know that the "watchman" will warn in time to find safety.
So the third analogy is that those who hear the watchman's warning that the "sword" is coming (punishment for sin is nigh) but do not flee (run from sinning, but "remain" in sin) have only themselves to blame for the chastisement.
In other words, those who ignore the legitimate Biblical prophets, not only during their time but in the future as scripture is read, are like people who ignore the warning call of the watchman, and thus, in not fleeing to safety, have only themselves to blame for the shedding of their own blood (or whatever form God's chastisement takes, which may well be in the form of being cast into hell upon one's sudden death).
Then God compares the good watchman to the negligent watchman.
6. But if the watchman see the sword come, and blow not the trumpet, and the people be not warned; if the sword come, and take any person from among them, he is taken away in his iniquity; but his blood will I require at the watchman's hand.
The only negligent prophet is the false prophet, as God has just explained that the true prophet is like a watchman who sounds the warning. False prophets do not warn the people of either their sins or of the impending certain chastisement. So they are truly like a watchman who looks the other way and does not warn when the sword comes. God explains that both the sinners AND the watchman-the false prophets or, to put it in modern terms, the negligent preachers or deniers of God-will be chastised.
Notice, then, how clearly God speaks and explains the role and responsibility to Ezekiel. Anyone who lived during those times would have totally understood this analogy. God then summarizes to Ezekiel.
7. So thou, O son of man, I have set thee a watchman unto the house of Israel; therefore thou shalt hear the word at my mouth, and warn them from me.
In other words, God has appointed Ezekiel the watchman for all of Israel, meaning that all the faithful MUST heed Ezekiel's warnings, given in full authority from God himself.
Far from being mysterious, you can see how clearly God explains not only his "doctrine," in the sense of how and what he expects from the faithful, but he also helps those he calls upon to fully understand their responsibilities. If you read the rest of Ezekiel 33 you will see that God continue to explain for many verses this very analogy of responsibility, repeating examples of those who heed the watchman and those who do not, and of the good watchman and his responsibilities, and the punishment that will be meted out to the negligent watchman.
There is no reason moderns cannot understand quite fully and clearly this warning. One need only think of the modern watchman, such as the technology of the burglar alarm, for a similar analogy. Who wants to sleep with a false burglar alarm, trusting in it when it does not work? That is what the assurances of the false prophet, or the unbeliever, or the "soft" preacher who does not understand that God can and will chastise for sin is like, a burglar alarm that says that the perimeter is safe and that one's family is secure, when in fact the very opposite is true. Blame must also be put on those who put their family in reliance of a faulty system, if one is to use this analogy in modern terms. In this case it would be like the family who deliberately does not place batteries in their fire detectors.
But you see, this is one reason the Bible is ageless. You should not update the Bible to modern analogies because they just do not, as you see above, capture the nuance of the personal relationships of citizens/watchman. It is the responsibility of the Bible reader to understand the analogy in the terms that God himself placed them in in the first place and thus one will be more likely to avoid error. There is no misunderstanding a negligent watchman, a human being, while moderns can split hairs over technical analogies (such as placing batteries in fire detectors) and thus try to word smith and tech analogy their way out of salvation and righteousness through inadvertent or deliberate misunderstanding.
I hope that you have found this helpful.