There are prophets ,preachers, teacher and evangelist. Prophets hear directly from God, preacher preach from the word of God, teachers teach the word of God and evangelist take the word of God to other churches and other countries. No one other than God the Father can know the exact time of His Son's returning, but Jesus said you can know the season by the signs of the times. Matthew 24 give you a list of signs to watch for to tell that the time is close, not the day or the hour, but the season. As in the days of Noah when sin was rampant, God took out the only righteous people to safety and flooded the earth to cleanse it of sin. Anyone that names the exact day or hour is a false prophet but anyone that points to the signs is doing what God expects us to do, warn the sinner so he/she can repent and be saved. If we don't warn them, then we can be held responsible. If they don't listen, then we are not responsible.