In this verse, the Apostle Paul summarises a personal experience he underwent after his salvation found in Acts 9:1-20. Paul was “alive apart from the law” when he came to saving faith in the Messiah. That was when he was freed from the Law. Only three days after becoming a believer, he knew what it was like to be filled with the Holy Spirit and to live a Spirit-filled life. However, because of his spiritual immaturity as a young believer, he had the misconception that he could then be sanctified by the Law. So having been freed from the Law through his salvation, Paul mistakenly put himself back under the Law, assuming he could now keep it. It wasn’t long before he noticed that he was failing and failing miserably. The Law proved he could not do it at all. In failing to keep the Law, he stood accused and found himself dying again. All of a sudden, the sin nature was revived, resumed its power over him, and he “died,” or became ineffective in his spiritual walk.
The application here is that when we try to live our new life in Christ on our own strength and based on our own self-created laws, the sin nature still dwelling in us (Romans 7:20) will exploit that as an opportunity to cause us to sin more (Romans 7:7-8). In other words, when we try not to sin — we will.
The Bible has many commandments for believers which we are obligated to obey without question, yet the means of fulfilling them is not by the power of the flesh but by the power of the Holy Spirit (Romans 8:1-14).