John Piper made that statement in the sermon I’d recently posted called "Be Killing Sin or Sin Wil Be Killing You", and we’ve shared it a couple of times in our Knowing God class at church. It’s quite a statement, and one that might come as a shock to some. His point is that if we’re okay with sin – we have a "peace-time mindset" or a "settling in with sin in our lives" if we’re okay with sin in our lives, that is COMPLETELY counter-cultural to having God’s Holy Spirit inside you as a believer. A true follower of Christ, when confronted with sin, will agree with what God’s Word says about it, and then – in Piper’s words, "KILL IT!" Romans 8:13 says, "IF by the Spirit YOU PUT TO DEATH the deeds of the flesh, you will live." Piper also says in a book or sermon that "the Christian life is a series of deaths. Some are small – like the death of ‘my time’ or how I spend my money or what I want to do. And some deaths are a laying down of one’s life – as a martyr." Simply put – if I am not fighting sin right now – I am NOT saved! I say that, because that’s what God says – now he doesn’t mean, that if on Monday I’m fighting but on Tuesday I’m not so I’m not saved on Tuesday. He’s saying that my life will be marked by fighting sin, not complacency towards sin. I need to be reminded of this battle, so that I don’t become fall into the decietfulness of sin and lose the war.
Here’s another video (you’ll have to excuse the lame graphics & cheesy christian music) of Piper talking about this topic. Don’t worry, it’s only a few minutes long, you can do it.