"Smite a scorner, and the simple will beware." --Proverbs 19:25
My life as a Christian started rather simply: I knew that my sins kept getting me into trouble, and that I couldn't stop sinning, and that Jesus could help me. So I called upon Him, and He has delivered me from the penalty and power of my sins. (I am eagerly looking forward to the day when He delivers me from the presence of sin.)
My life as a Christian has continued in simple fashion: if it doesn't agree with the Bible, it's wrong. Now, atheists like to tell me that that is a stupid position to take, but I have lived my life this far and never been led astray by Scripture. In fact, everytime that I have believed something other than what Scripture said, I have found that thing to be false and myself to have erred, in the practical things of life. So, why not believe it for everything? Simple enough.
Sin is also a pretty simple issue: if God says don't do it, you will pay dire consequences if you do. Drug abuse and fornication are two sins that have plain-to-see (unless you're an atheist) serious consequences, consequences that frightened me into praying never to fall prey to those sins. By the grace of God, I never have. Drug abuse just isn't appealing to me, and God has simply never let me commit fornication (and I am so glad!)
Rebuke is rather simple, as well: If I know that someone put poison in your cup and I don't tell you before you drink from it, then I am just as guilty of murder as the person who actually put the poison in the cup. So, if I let you go down the road of sin and I don't tell you about the consequences, then I am just as bad as the devil who is trying to destroy you.
This last point is misunderstood by many of my Christian friends. They believe that I am judging them when I point out their flaws. I believe that I am warning them about the trap that Satan has laid for them. Perspective is everything. And I dearly hope that I can communicate this just a little better to my dear friends.