I think that the “I” in Romans 7 is Paul, identifying with unbelieving Jews under God’s law. Paul is recalling the true state of every Israelite under God’s law. Though Paul is a Christian Jew, he writes in words that are true for non-Christian Jews: “For I have the desire to do what is good, but I cannot carry it out” (Rom 7:18b). Here are some reasons why I think this interpretation best fits Romans 7:
(1) The context is Paul’s response to a Jewish objection, so it is appropriate that he has unbelieving Jews in mind. His comment in Romans 7:5 (“the sinful passions aroused by the law”) would have caused a double-take from the first-century Jew. The law, provoking evil passions? It seemed unthinkable! So Paul’s explanation in Romans 7:7-25 has to demonstrate that–for unbelieving Jews–the Law of Moses aroused evil passions.
(2) Paul quotes from the Law of Moses, which non-Christian Jews received at Mount Sinai. He cites the tenth commandment in Romans 7:7b: “Do not covet.” His comments, then, recall the occurrence at Mount Sinai.
(3) The statements about “the commandment” recall God giving the Law of Moses at Mount Sinai. In Romans 7:12, Paul equates “the commandment” with “the law.” He says, “the law is holy, and the commandment is holy, righteous and good.” So when Paul says “commandment” in Romans 7, that is another way of saying the “law” of Moses. Thus, “I found that the very commandment that was intended to bring life actually brought death” can be understood to mean, “The Law of Moses that was intended to bring life actually brought death.” This was the true experience of every Israelite.
(4) The statements about delighting in God’s law–but being unable to fulfill it–were true of unbelieving Jews. “For I have the desire to do what is good, but I cannot carry it out” (Rom 7:18b). This refers to every Jews’ desire to obey the Law of Moses, but failing to do it nonetheless. “For in my inner being I delight in God’s law” (Rom 7:22) recalls Psalm 1 and Psalm 119, where the faithful Israelite delighted in God’s law–but, even the most faithful Israel could not keep it perfectly. For, “When I want to do good, evil is right there with me” (Rom 7:21).
(5) A pious unbelieving Jew was a slave to God’s law in his mind. “So then, I myself in my mind am a slave to God’s law, but in the sinful nature a slave to the law of sin” (Rom 7:25b). This verse expresses the genuine struggle for every non-Christian Jew. While their minds wanted to obey the Law of Moses (given to the Israelites at Mount Sinai), they remained slaves of sin and death, and thus they could not fulfill God’s law. “For what I do is not the good I want to do; no, the evil I do not want to do–this I keep on doing” (Rom 7:19).
In summary, the “I” of Romans 7:7-25 is Paul writing about his pre-Christian status as a Jew, identifying with every Israelite who lived under the Law of Moses. Paul is not writing as a Christian who is struggling with sin and is constantly defeated by it. The believer is not enslaved to sin any longer, but the unbelieving Jew is a slave to sin. Paul’s words in Romans 7:7-25 recall the situation of slavery that was true for every Israelite–but not for the Christian, who has been freed in Christ Jesus.