16 Now if I do what I do not want, I agree with the law, that it is good. –  εἰ δὲ ὃ οὐ θέλω τοῦτο ποιῶ, σύνφημι τῷ νόμῳ ὅτι καλός.– He notes that although he often sins, the very fact that he agrees with and approves of the good statutes of the Law indicates that a change in principles within him has come about.
17 So now it is no longer I who do it, but sin that dwells within me.–  Νυνὶ δὲ οὐκέτι ἐγὼ κατεργάζομαι αὐτὸ ἀλλὰ ἡ ἐνοικοῦσα ἐν ἐμοὶ ἁμαρτία. – Paul states once again here that he disavows the sinful identity to which he once again as an unbeliever. His use of κατεργάζομαι here indicates that he no longer regards himself as a sinner, as someone continually enslaved by and in bondage to sin, but as someone who is a new creation in Christ. Nevertheless, he is not perfect and continues to struggle against sin.
18 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. –  οἶδα γὰρ ὅτι οὐκ οἰκεῖ ἐν ἐμοί, τοῦτ᾽ ἔστιν ἐν τῇ σαρκί μου, ἀγαθόν: τὸ γὰρ θέλειν παράκειταί μοι, τὸ δὲ κατεργάζεσθαι τὸ καλὸν οὔ: – When Paul says that he knows that nothing good dwells in him, and qualifies it with “that is, in my flesh”, it is likely that he is saying that although there is nothing inherently good about him following his primordial fall in Adam into sin, the Holy Spirit within him continually works righteousness in him. We must once again understand κατεργάζεσθαι as an exaggerated, frustrated cry of a converted Christian who genuinely wants to be completely delivered from the war between sin and holiness which rages inside of him.