There are plenty of reasons why you do not already do whatever you want out of fear of the law, and you will find these reasons persist and remain long after the gospel has its way with you.
“So I can just do whatever I want now that I’m a Christian?”
I have concluded that if you’ve never been asked this question, you have never preached the gospel as Paul preached it because Paul got asked this question a lot. He addresses this question in many ways throughout his epistles, but most famously and perhaps a bit most directly and effectively in Romans 6-7. More on that in a minute because I want to ask you a question in return: What keeps you from doing what you want right now?
For me, it’s often my old adam, my old sinful nature, which works to preserve my reputation, my respectability, and a good deal of self-righteousness. It’s got all sorts of answers as to why I should not act on every impulse that comes my way, and not one of them has to do with loving God or my neighbor as myself, nor does it ever concern itself with what God might say on judgment day. Instead, most often, my answers have to do with loving and respecting myself, wanting to stay out of jail, avoiding another broken marriage, not wanting to be ostracized by friends and family, the list goes on and on. I imagine these answers look the same as that of many atheists, agnostics, and other non-Christians who live more or less moral lives in line with the rest of what society deems acceptable, and all of whom I imagine also work to keep in check those same reptilian impulses of an adolescent mind.
This is the natural law at work. This is why God has written his law on the hearts of man, because in this way, a modicum of peace is kept in society. The forgiveness of sins does not remove the machinations of natural law at work in this world any more than it removes a felon from jail or administers a pardon to a death row inmate because he supposedly found Jesus. In other words, there are plenty of reasons why you do not already do whatever you want out of fear of the law, and you will find these reasons persist and remain long after the gospel has its way with you.
Of course, I also know my own history does not exactly show these reasons have been adequate enough to keep me from doing what I know to have been wrong. However, this is not confession time. I will suffice it to say that I can honestly confess with the rest of my congregation on Sunday morning that I am a poor miserable sinner. There are many sins that haunt me from the past, and I am rather convinced those are not even the worse ones. Maybe that’s the Holy Spirit at work. I say this as one who does not get to right off adolescent adventures as something I did before I became a Christian. I have been a Christian all my life. I have never had to go a day without knowing the forgiveness of sins. I was baptized within hours of birth and have walked in the newness of life for going on 46 years, and just for that reason, I have never done solely what I have wanted to do. Instead, I have lived my entire life as Paul describes the Christian life in Romans 7:
For I do not understand my own actions. For I do not do what I want, but I do the very thing I hate. Now if I do what I do not want, I agree with the law, that it is good. So now it is no longer I who do it, but sin that dwells within me. For I know that nothing good dwells in me, that is, in my flesh. For I have the desire to do what is right, but not the ability to carry it out. For I do not do the good I want, but the evil I do not want is what I keep on doing. Now if I do what I do not want, it is no longer I who do it, but sin that dwells within me (Rom. 7:15-20).
That’s the twist! When you receive the Holy Spirit, your wants are changed. But they are not always changed completely overnight. As you grow and mature in the faith, you find yourself desiring higher gifts and a still more excellent way (1 Cor. 12:31) which is still out of reach. You find that you want to love God with all your heart, with all your mind, and all your might. You want to love your neighbor as yourself, not out of self-protection but out of genuine love. You also find that you have failed to do this in any meaningful or objective manner. You still find yourself in petty squabbles with others, your spouse, your children, your parents, your coworkers. You find that you struggle with sins that embarrass you and which you still do. Sometimes you find that all the “good” you thought you were doing you did for yourself, and you take it hard when others are not appreciative. You also find that all the new reasons you have for not doing what you know to be wrong can be just as ineffective as the old reasons. In other words, you still find you are a sinner, even though you are also a saint.
You are a saint. You walk in the newness of life. You walk in the forgiveness of sins. You grow in the faith and mature in understanding and wisdom, even though you may often fail to recognize such growth. No, you no more get to do what you want now that you are a Christian than you did when you were not. But that is alright because Jesus is faithful even when we find that we have been faithless. Jesus did not just die for sinners on the cross; he also died for saints. Now you walk in his resurrection, even as you hobble in your sanctification.