Ezekiel33:7 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. KJV
A sentinel is a guard whose job is to stand and keep watch. If you watch some of the epic Korean films like: Conqueror and Jumong, you'll see sentinels. In ancient cities with walls, sentinels are placed at strategic points on the city wall to watchover the city. Their job is to warn the people about a pending danger. Often times, they look afar to see if the enemies are coming to wage a war against their city. If confirmed, they'll warn the people on time so that the city gates can be closed against the enemy.
God has placed you as a watchman over the people. Every watchman is responsible for the blood of the people if he doesn't warn them of a pending danger. You are God's sentinel on the earth. If you understand your role as a watchman, you'll never cease to preach the gospel and to warn sinners about God's coming wrath. "Knowing therefore the terror of the Lord, we persuade men; but we are made manifest unto God; and I trust also are made manifest in your consciences"(2Cor5:11).
Warning sinners is part of the gospel and that's the major work of the sentinel. In as much as we preach God's grace and love to sinners, we need to also let them know the consequences of rejecting the offer of free salvation. Failure to discharge our duties as kingdom sentinels would make God require the blood of sinners from our hands. Paul knew this truth, that was why he said, "I declare today that I have been faithful. If anyone suffers eternal death, it’s not my fault"(Acts20:26). Can we speak boldly like Paul that we won't be at fault if unbelievers around us suffer eternal death in hell?
Paul didn't watch sinners go to hell, he rescued them by preaching the gospel. You owe sinners the duty of preaching the message of God's redemptive love and to warn them of his wrath that is to come.