Paul was addressing Romans that believed the gospel from the heart even though they were servants of sin. The moment they believed the gospel they were set free from sin.
Paul is showing that a sinner can believe the gospel as he is, and does not need to be regenerated to have the ability to believe as you falsely teach.
You don't understand because you don't want to understand.
Now, how many times are you going to ask the same questions? Do you have a learning disability?
How can a sinner believe in Jesus and yet not be regenerated?