Paul has a desire to obey God, but at times he also has a desire to do things that God hates. He writes of the two desires he has as if they were two men fighting each other. (See: [[rc://en/ta/man/jit/figs-metaphor]])
These words refer to the natural human desire to rebel against God and disobey him. Paul calls this a law because he has observed that this is the way people live. It is not a collection of written commands.
The phrase "the members of my body" is another way of saying "my flesh" ([7:18](./18.md)), which is a metaphor for the old nature, opposed to God, with which Paul was born. Here it is a metonym for the actions people do because of that old nature. Alternate translation: "in my actions" or "in my behviors" (See: [[rc://en/ta/man/jit/figs-metaphor]] and [[rc://en/ta/man/jit/figs-metonymy]])
This "law of sin" is the same as the "different law," the natural human desire to rebel against God and disobey him. Paul calls this a law because he has observed that this is the way people live. It is not a collection of written commands.