Luke 9: 23
Then He said to them all, “If anyone desires to come after Me, let him deny himself, and take up his cross daily,[a] and follow Me. 24 For whoever desires to save his life will lose it, but whoever loses his life for My sake will save it. 25 For what profit is it to a man if he gains the whole world, and is himself destroyed or lost? 26 For whoever is ashamed of Me and My words, of him the Son of Man will be ashamed when He comes in His own glory, and in His Father’s, and of the holy angels.
These words of our Lord and Savior Jesus Christ should not be taken lightly. The life of the Christian is one of spiritual warfare, denying ourselves and our sinful fleshly impulses for the sake of Christ and His righteousness. The way we do that, of course, is by the power of the Holy Spirit, for we cannot find the goodness to obey Christ and take up our cross in and of ourselves. This is why Christ took up the cross for us. We are simply following in His footsteps, by the power of His Spirit, putting to death the deeds of the flesh. It is a privilege to be empowered to fight against sin. God could have completely sanctified us as soon as He saved us. But, in His infinite wisdom, He has chosen that we should fight the remaining indwelling sin that is within us, sin that has already been crucified for us by Christ (Gal. 5:24-26).
So we are warring against sin that, in reality, has no dominion or power over us any longer. All sin has been crucified. I've often wondered what that might mean. Crucified means dead right? Yes, and no. It is evident that my sinful nature remains in me, that it is indeed still alive and kicking. And it is not that it is in the process of being crucified by Christ- for Christ clearly died once for all. The work on the cross has been finished; we are free from the wages of sin because Christ paid the wages of sin, death, for us.
From what my little brain can muster, it would seem to me that sin is dead to me, all sin, including my remaining indwelling sin, in the sense that it holds no claim on me any longer. Yes, my flesh still cries out to lust after that girl, or to be impulsive, rude, arrogant, and the like, but the sting of sin, death, punishment, hell, is gone. And in that sense, sin has been crucified. It has been paid for. I still struggle against my sin nature, and battle against sin, and I am to take up my own cross and crucify this remaining sin, but I am not crucifying it in the same sense that Christ crucified sin. Obviously if I were, then Christ did not actually atone for me, and the Bible would be commanding me to atone for myself. So the sense in which we are to crucify the deeds of the flesh is in the spirit of Christ, but not in the actual event of Christ or for the same exact purpose. What I mean is, sin is dead to me- it cannot kill me, it cannot rule over me. It has been crucified, by Christ, on the cross, once for all, forever. So my sin has been crucified, killed, as it were. Yet, this body of sin, which I still have, remains. The Spirit is giving life to it, growing me in sanctification (Romans 8:11). And yet, while the Spirit grows me, it does not grow me by me remaining passive. No, it grows me by giving me the means and willpower to put to death the sinful deeds of the flesh. It works through the Truth of Scripture, in other words, true theology (John 17:17), inclining my heart to the precepts and truths and teachings of the Word of God. The Spirit of Christ and the regenerate heart incline me to love what is true, the pleasures of living for what is good and righteous, rather than living for the passing pleasures of sin- that which is tied up with the sinful impulses of the flesh.
And it is in that way which the Spirit beats down the sinful flesh. The flesh will always cry out for more sin. Galatians 5:
I say then: Walk in the Spirit, and you shall not fulfill the lust of the flesh. 17 For the flesh lusts against the Spirit, and the Spirit against the flesh; and these are contrary to one another, so that you do not do the things that you wish. 18 But if you are led by the Spirit, you are not under the law.
This is very similar to what Paul says of himself in Romans 7, that what he hates is what he does, and what he does is that which he hates. Now here in Galatians, as well as Romans 8, we learn that those who are led by the Spirit are not under the law and are the true Sons of God. In other words, those whom live by the Spirit and put to death the deeds of the flesh are the ones who are truly saved. This is precisely what Christ meant when he said to take up the cross and follow Him. We are not killing sin in order to crucify it- that is to say, we are not killing sin in order to save ourselves, or to keep our salvation. Rather, we are killing sin that has already become dead to us by the cross of Christ. We are fighting the impulses of our sinful nature that is crucified to us, that no longer can damn us. So, the question becomes then, what is the motivation for killing sin, since it has no power over us any longer?
The answer to that, I think, is very important. For the true Christian, led by the Spirit of God and walking in the Spirit, their motivation for doing so is simply that they want to do so. In other words, they love God. There is no ulterior motive. You may be able to make some kind of plea to being rewarded in heaven, but I would wager that no one who is a true Christian finds their sole or root motivation for obeying Christ and taking up their cross to kill sin by the Spirit's power as simply a means to gain greater rewards in heaven. If you took away all the rewards in heaven, a true Christian would still serve God and take up the cross against themselves and their sin, simply because they love God. Their hearts have been changed by Him, the Spirit convicts them, they have a new, repentant mindset that sees sin as their mortal enemy and Christ as their greatest friend and ally.
Not to mention, our rewards in heaven are really nothing more than God crowning His own graces to us, and hence we will cast our crowns, our rewards, back at His feet (Rev. 4:10). So the motivation, or the right motivation at least, for even desiring reward in heaven is simply to please God by casting the rewards back at His feet. So those who desire reward in heaven for selfish reasons, to have a "glittering crown on their brow," aren't desiring rewards for the right reasons, and thus, their motivation is sinful. They wouldn't cast their crowns back at the feet of Jesus, because they don't understand that the rewards are His, and His alone, to begin with. These types of people will, I have no doubt, find that they remain in their sins on the Day of Judgment.
So why do we take up the cross, dear Christian? We take it up because we love Him, our Lord and Savior, Jesus Christ. We take it up because it is our calling, our privilege. In fighting sin, we get to learn what it is like to hate sin, to oppose sin, to defeat sin, to "crucify" the sin that has already been crucified for us. In the same way that God honors us and gives us the great gift of praising Him through worship and music, God gives us the honor to glorify Him and praise Him with our lives, fighting against the sin that cannot harm us any longer. So we get to show our love for God by fighting against this crucified sin, not because it will save us or reward us, but because we want to show God how much we love Him for His grace and mercy to us, and because we want to learn how to be obedient. With this heart and mindset, it is no wonder that when God crowns us, we give Him the crown right back, for that is what we wished to do all along. I don't want to go to heaven without receiving a crown, not because I want to wear a fancy crown on my head and brag, but because I don't want to have no gifts to give back to God and my Lord and Savior Jesus Christ.
And this, I believe, is our chief motivation for taking up the cross. To please God, to show our gratitude, to increase His glory and our joy, to proclaim His fame. It is what we have been called to as Christians. We do not wish to neglect so great a salvation. We want to war against our sin, running with endurance "the race that is set before us, looking unto Jesus, the author and finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God." (Hebrews 12:1b-2). And we know that we are running a race that has already been won, and that we will most assuredly complete and endure as well, for Christ endured it for us already, and it is His enduring Spirit that is within us, driving us on, beckoning us to take up the cross against already crucified sin.