Obligation to tell the hard Christian truth?

Last Sunday at church, a fellow church mate of mine who is quite active in the leadership ministry of the youth service gave his maiden sermon. The message of his sermon was about how we need to tell the hard truth about God’s punishment for sin to the world, even though this message is displeasing to people out there. He brought up the passage featuring the prophet Jeremiah, who spoke the bitter prophecy about Israel’s future exile, and contrasted this with the more optimistic sounding albeit false prophecy by Hananiah in the passage of Jeremiah 28. The point of this biblical passage is that the good news is not necessary the truth.

I wonder how I should relate to the sermon message for that day. The speaker was saying that if you talk to people about how they are in sin, and that Jesus is the only way to be saved, they would scorn you for being judgemental and exclusive. He then went on to cite the verse about how it is only natural for Christians to be persecuted for their message.

For the most part, I don’t see it as my business to tell people who are living sinful life to repent and turn to God. If I have the opportunity, I prefer to tell them about my Christian faith, and introduce them to a friendly loving image of what it is about, and then let them accept the doctrines on sin and punishment by themselves once they start attending church. I do acknowledge that we live in a sinful world with sinful people, and that I am myself someone who struggle with sin. I think that Christianity has a good message to preach in telling people to avoid living a sinful life. But I think I will just come off as an overzealous religious nut if I tell people that they are sinful and need to repent right in their face. And I don’t exactly like invoking the doctrine of hell and punishment as a way for people to acknowledge their sins and repent of them. I think sin should be avoided for its own sake, more than just out of fear of punishment.

I also am not sure how to carry out this Christian obligation, if indeed it is a Christian obligation, in a socially appropriate manner. For example, if I am sitting with school peers who are non-Christian and they are talking things which are lewd at the lunch table. I don’t join in with such conversation if it gets too lewd, but I don’t want to appear self-righteous or overly-holy either by telling people that such conversation is not something I like or condone from my Christian convictions