What do people really mean when they say, “Jesus is my life”? What did Paul mean when he said, “it is no longer I who live, but Christ who lives in me” (Gal 2:20)? To understand what this means—like so many other things in Christianity—we must understand sin.
We need to read what the apostle Paul says about sin in Romans 7. What he says in Romans seems to contradict what he says in Galatians. The apostle Paul—who said Christ lives in him—also said, “I am not practicing what I would like to do, but I am doing the very thing I hate [i.e. sin]” (Rom 7:15b). Christ does not sin. Christ lives in Paul. Paul sins. How do all those seemingly contradictory statements fit together? When we put these things together, I think we can understand what life in Christ is. Ironically, these pieces need not fit well for this to work. Let me try to explain:
For Paul, the reality of sin in his life pushes him toward Christ. It is not only Paul’s sanctification that causes him to say Christ lives in Him but also his sinfulness. Just like the unstoppable laws of nature, Paul finds a law in him (Rom 7:21). This “law” says, “Paul will sin,” and it is as reliable as the law of gravity. Of course, this law is very much at odds with the reality that Christ lives in him since Christ’s law is that “Christ will not sin.” And that is even more reliable than gravity. This tension, or in the words of John Murray, “contradiction” in Paul causes him to experience Christ as his whole life. This necessity for Christ to be everything is because everything in Paul that is not Christ is evil. This is so much the case that the evil within his flesh is like a “law.” It always happens. The part of Paul that is not Christ is in “bondage under sin” (Rom 7:14). In other words, without Jesus, Paul = sin.
So, when Christ comes to dwell in Paul, he has a new experience of sin. Namely, the sin in Paul becomes something else. It is no longer Paul who is sinning: “So now it is no longer I who do it, but sin that dwells within me” (Rom 7:17).
This idea that it is not Paul who is sinning is a very important point: the only way that everything said above can be true is if Paul starts to exist as Christ. Since Paul = sin and Christ lives in Paul, for Paul to not = sin, Christ must be the one who truly exists. In other words, for Paul to live a good life, he must stop existing as Paul and start existing as Christ. So, Paul has been united with Christ, and therefore, the sin in Paul is not him anymore. To be sure, there is still sin in Paul’s life, but Paul says that is not really who he is (Rom 7:17). Why? Because Christ is his life.
Practically speaking, this means that Paul’s experience of life goes something like this. He does sinful things. Because Christ lives in him, he really hates those sinful things he does. When he experiences that grief over sin, he looks to Christ and says, “I do not exist apart from you. Everything I do apart from you is not really me. My whole life is Christ.” Or, in the words of John Calvin, “The whole man, so far as relates to the flesh, must be reduced to nothing, that it may be renewed according to God.”
When Christians inevitably sin, we should look to Christ and tell Him that we do not want to exist in any way apart from Him. We should say to Him that we do not want to have thoughts, glances, or even feelings that are not Him. The only way a Christian exists is Christ. He owns us. He is our Master. He commands us. He lives in us. He created us. He plans our lives for us. He is our All in All. That might sound like a bad thing until you experience the utter grief of sin. When you do—when you feel the eternal disgust of sin—you look to Christ and say, “I no longer live, but Christ lives in me.” In this way, true-full life in Christ only comes when we understand our own sinfulness. It is the sin piece of the puzzle that helps us understand the life-in-Christ piece of the puzzle.
This need to understand our sinfulness is why conviction of sin is such a wonderful gift. In other words, sin is the prod of God, sharply pointing Christians to Him and away from the eternal torment of unchecked sin. Sin in this life is like inoculation—it is a small dose intentionally administered in order to prevent the same substance from completely taking over our lives. It hurts, but the destination it points us to is Life itself. But it is also dangerous. If we take too big of a dose, parts of us might need to get cut off. We may still live, but the inoculation can cause severe damage if we do not follow instructions. The role of sin pointing us to Christ is why God allows us to struggle with sin in this life. He could do away with all our sin-habits in a snap. But He leaves the vipers so that their bites send us to Christ.
We miss out, therefore, when we run from conviction of sin. When we sin and brush aside the pain in our hearts, we brush aside Christ. That pain is there to point us to Christ. If we do not feel the pain of conviction—the bites of the vipers—then we think we do not need Christ. Or, at least, we think we need Him less than we do. The need to recognize our sinfulness and feel its conviction is why churches that do not teach about sin do not create Christians who love Jesus more than anything. To know the pain of sin is to know the treasure of Christ. To ignore the pain of sin is to miss out on true life in Christ. In other words, the conviction of sin is the mechanism by which we “jump out of ourselves” and get “into Christ.” The conviction of sin is your Friend.
Bono is one of the most famous rockstars in the world. He is also a Christian. In a recent interview for Christianity Today, he spoke about being uncomfortable in his skin, even being nervous talking to a group of High Schoolers. “To be yourself is the hardest thing,” he said. “I’ve never once been myself.” He expounded, “The integratedness you expect from a person who’s been made whole by their faith, I’m probably missing. I have the joy, I have some insights, I have a lot. But being comfortable in my skin is what I was talking about.”
I think Paul meant something similar when he said, “I know that nothing good dwells in me, that is, in my flesh” (Rom 7:18). If our flesh is sinful, it stands to reason that we will not be completely comfortable in our own skin. As long as Christ has not completely taken over our lives, there will be an unstable and longstanding pressure on our hearts and minds. Though we do not like it, this is part of God’s plan for this world. We will be uncomfortable until we are fully in Christ. Our hearts will be restless until they find their rest in Him.
“So, my brothers, you also were made to die to the Law through the body of Christ, so that you might be joined to another, to Him…” (Romans 7:4a, LSB)
 John Calvin and William Pringle, Commentary on the Book of the Prophet Isaiah (Bellingham, WA: Logos Bible Software, 2010), 208.