On Wednesdays, we dive back into the 1,200 sermons we have of Pastor John's at DesiringGod.org and pull out some choice clips from some old messages. The following clip is taken from John Piper's sermon, "Battling the Unbelief of Lust," which he preached 25 years ago on 1 Thessalonians 4, verses 1 to 8.

In the sermon, he explains why sexual sin is an act of unbelief. Here's what he said. I'm trying to explode the doctrine that the battle for obedience is optional because only faith is necessary for salvation. This is very tricky, the way words are used here. Here's my response. The battle for obedience is absolutely necessary for salvation because it is the fight of faith.

The battle for obedience is absolutely necessary for getting to heaven because it is the battle against unbelief. It is the fight of faith. There are not two battles. One, to get yourself saved by a single act of faith, and the other, to collect rewards by works. There is only one battle.

It's the one that gets you started. It's the one that gets you there. And it's the fight of faith, not works. Faith is what severs the root of covetousness, misplaced shame, anxiety, lust, and tonight, envy, and six more before we're done this year. There is one warfare, and it is the warfare of faith.

Let's go to verse 5, and I'll try to demonstrate for you why I think this text teaches that the root cause of lust is unbelief. Verse 5 says, "Take a wife or control your body, not in the passion of lust, like the heathen or the Gentiles who do not know God." Now, do you see what that implies about the root of lust?

Not knowing God is the root cause of lust. Not knowing God is the root cause of lust. Now, what does that mean? Let's just think about this. What kind of knowledge is he talking about? Do you remember how much the demons knew in the ministry of Jesus? Do you remember in Mark 1 24, Jesus comes into a synagogue, there's a man there with an evil spirit, Jesus is ready to cast out that evil spirit, and out of the mouth of that demon-possessed man comes the words, "I know who you are, the Holy One of God." The disciples didn't even know that.

Do you realize how much the demons know? How accurate and large is their knowledge of God on many things, and yet they seethe with lust. So that's not the kind of knowledge that's being spoken of here. You can pack your head with theological knowledge and go straight to hell.

I used to go to professional theological meetings. I remember one in St. Louis, and St. Louis has some pretty gross and grisly sexual streets in it. And what these men who teach theology in the universities around this country did, there is no connection between mere head knowledge and the power of godliness.

Mere head knowledge. So what does he mean when he says, "When you give in to lust, you act like the Gentiles who don't know God." It's a different kind of knowledge. It's the knowledge described in 2 Corinthians 4, 6, where he says, "God has shown into our hearts to give the light of the knowledge of the glory of God in the face of Christ." It's the knowledge of God's greatness, His grandeur, His glory, His beauty, His power, His wisdom, His justice, His goodness, His truth.

It's a knowledge that humbles you and wins you and holds you. It's the knowledge of God that is very unlike mere head knowledge. It's the knowledge that you don't have when you say, "Ho hum" during the Hallelujah Chorus. It's the knowledge that you don't have when you grumble on the rim of the Grand Canyon at sunset, hearing they do not hear and seeing they do not see.

It's the knowledge that you have when you're like Lydia and the Lord has just opened the heart to give heed to the glory of God in the face of Jesus Christ in the Gospel. It's the knowledge that wins, holds, humbles, ravishes, enlightens, delights. It's the knowledge of faith, the assurance of things hoped for, the conviction of things not seen.

That's the knowledge that liberates from lust, the knowledge which is faith. It's a knowledge so real and so precious and so satisfying to your soul that when any attitude or emotion or thought or addiction threatens to diminish your capacity to have and enjoy that knowledge, you fight it as though your very life were threatened, which it is.

Do you remember 1 Peter 2, 11? "Abstain from lustful passions that wage war against your soul." Your life is at stake in the way you fight your enemy called lust. That clip was taken from John Piper's sermon, "Battling the Unbelief of Lust," which he preached on November 13, 1988.

He develops this connection between lust and unbelief more fully in his book, "Future Grace." There, Pastor John writes, "The battle against lust is absolutely necessary for our salvation because that battle is the battle against unbelief." That's from chapter 27 of his book, "Future Grace." You can find more information about the book on the book page we have at DesiringGod.org.

Click on "Books" and then click on the title, "Future Grace." Well, as we have mentioned recently, this week we host our 12th and final national conference here in Minneapolis. Look at the book, "Reading the Bible for Yourself." It should be a wonderful conference. Well, reading the Bible for ourselves is often just a matter of time.

So how can a busy mom with young kids and a full schedule find the time she needs to read her Bible? Tomorrow, Pastor John will offer some very practical advice to this mom. I'm your host, Tony Reinke. We'll see you tomorrow on the Ask Pastor John Podcast.